Class 10 Science · Chapter 4

Carbon and its Compounds

442 Class 10 Science questions on Carbon and its Compounds from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 14 of 23

1. Q261 CBSE 2022
   Draw two ​structural ​isomers of ​butane.
   Show answer

   The two structural isomers of butane, ${\text{C}}_4{\text{H}}_{10}$, are n-butane (straight chain) and isobutane (branched chain).

   The two structural isomers of butane, ${\text{C}}_4{\text{H}}_{10}$, are drawn in the figure: (1) n-Butane, the straight chain ${\text{CH}}_3{\text{–CH}}_2{\text{–CH}}_2{\text{–CH}}_3$: four carbons in one unbranched chain; each end carbon carries three hydrogens and each middle carbon two. (2) Isobutane (2-methylpropane), the branched chain ${\text{CH}}_3{\text{–CH(CH}}_3{\text{)–CH}}_3$: a chain of three carbons with the fourth carbon on the middle one, which carries one hydrogen; each of the other three carbons carries three. Both have four carbon and ten hydrogen atoms with four bonds on every carbon: the same molecular formula with different structures.

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2. Q262 CBSE 2022
   Consider the following molecular formulae of carbon compounds :

   1. (i)${\text{CH}}_3\text{COOH}$
   2. (ii)${\text{CH}}_3\text{OH}$
   3. (iii)${\text{C}}_2{\text{H}}_6$
   4. (iv)${\text{C}}_3{\text{H}}_4$ ​
   5. (v)${\text{C}}_4{\text{H}}_8$ (a) Which ​one of these compounds belongs to homologous series of alcohols ? (b) Identify the compound having triple bond between carbon – carbon atoms. (c) Write the molecular formula of the first member ​of ​the homologous series to which ${\text{CH}}_3\text{COOH}$ belongs. (d) Write the general formula of the series ​to ​which the compound ${\text{C}}_4{\text{H}}_8$ belongs.
   Show answer

   Methanol is the alcohol; ${\text{C}}_3{\text{H}}_4$ has the triple bond; the first acid is $\text{HCOOH}$; the alkene formula is ${\text{C}}_n{\text{H}}_{2n}$.

   (a) Methanol, ${\text{CH}}_3\text{OH}$, belongs to the homologous series of alcohols. (b) ${\text{C}}_3{\text{H}}_4$ (propyne, $\text{H}-\text{C}\equiv \text{C}-{\text{CH}}_3$) has a triple bond between two carbon atoms. (c) The first member of the carboxylic acid series is methanoic acid, $\text{HCOOH}$ (molecular formula ${\text{CH}}_2{\text{O}}_2$). (d) ${\text{C}}_4{\text{H}}_8$ belongs to the alkene series, whose general formula is ${\text{C}}_n{\text{H}}_{2n}$.

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3. Q263 CBSE 2022
   Draw ​the electron ​dot structure of ​the ​following :

   1. (a)​Benzene
   2. (b)Ethane
   Show answer

   Benzene: ring of six carbons with alternate double and single bonds; ethane: carbons joined by one shared pair, all bonds single.

   (a) Benzene, ${\text{C}}_6{\text{H}}_6$: six carbon atoms in a ring, each bonded to one hydrogen atom. Each C–H bond is one shared pair (one electron from C, one from H). Round the ring the carbon–carbon bonds alternate: three double bonds (two shared pairs each) and three single bonds (one shared pair each). Every carbon has 8 electrons round it and every hydrogen 2; there are 15 shared pairs, 30 electrons in all. (Drawn in the first figure.) (b) Ethane, ${\text{C}}_2{\text{H}}_6$ (${\text{CH}}_3$–${\text{CH}}_3$): the two carbons share one pair, and each carbon shares one pair with each of its three hydrogens: 7 shared pairs, 14 electrons, all single covalent bonds. Each carbon has 8 electrons round it and each hydrogen 2. (Drawn in the second figure.)

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4. Q264 CBSE 2022
   Consider ​the carbon ​compounds having following molecular formula :

   1. (i)${\text{C}}_2{\text{H}}_2$ ​
   2. (ii)${\text{C}}_2{\text{H}}_6$
   3. (iii)${\text{C}}_3{\text{H}}_7\text{OH}$
   4. (iv)${\text{C}}_2{\text{H}}_5\text{COOH}$
   5. (v)${\text{CH}}_3\text{CHO}$ (a) Identify ​which one of the above compounds, is a member of aldehyde series. (b) Write the general formula of the series ​to which compound ${\text{C}}_2{\text{H}}_2$ belongs. (c) Which one of the above compounds has ​triple bonds between carbon – carbon atoms ? (d) Write the molecular formula ​of the first member of the homologous series to which the compound ${\text{C}}_3{\text{H}}_7\text{OH}$ ​belongs.
   Show answer

   Aldehyde: ${\text{CH}}_3\text{CHO}$; alkyne formula ${\text{C}}_n{\text{H}}_{2n-2}$; triple bond in ${\text{C}}_2{\text{H}}_2$; first alcohol is ${\text{CH}}_3\text{OH}$.

   (a) Compound (v), ${\text{CH}}_3\text{CHO}$ (ethanal), which carries the aldehyde group $-\text{CHO}$. (b) ${\text{C}}_2{\text{H}}_2$ is an alkyne; the general formula of the alkyne series is ${\text{C}}_n{\text{H}}_{2n-2}$. (c) Compound (i), ${\text{C}}_2{\text{H}}_2$ (ethyne): $\text{H}-\text{C}\equiv \text{C}-\text{H}$. (d) ${\text{C}}_3{\text{H}}_7\text{OH}$ is an alcohol; the first member of the alcohol series is methanol, ${\text{CH}}_3\text{OH}$ (molecular formula ${\text{CH}}_4\text{O}$).

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5. Q265 CBSE 2022
   The molecular ​formulae of two alkynes, A and B are ${\text{C}}_x{\text{H}}_2$ and ${\text{C}}_3{\text{H}}_y$ respectively.

   1. (a)Find ​the values ​of $x$ and $y$.
   2. (b)Write the names of ​A ​and B.
   Show answer

   $x=2$ and $y=4$; A is ethyne and B is propyne.

   (a) $x=2$ and $y=4$, since an alkyne is ${\text{C}}_n{\text{H}}_{2n-2}$: $2x-2=2$ gives $x=2$, and $y=2(3)-2=4$. (b) A, ${\text{C}}_2{\text{H}}_2$, is ethyne (commonly called acetylene); B, ${\text{C}}_3{\text{H}}_4$, is propyne.

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6. Q266 CBSE 2022
   Write ​the chemical formula of two ​consecutive ​homologous ​of organic compounds having functional group $-\text{OH}$. What happens to the

   1. (i)boiling point and
   2. (ii)solubility of organic compounds of a homologous ​series as ​the molecular mass increases.
   Show answer

   ${\text{CH}}_3\text{OH}$ and ${\text{C}}_2{\text{H}}_5\text{OH}$; boiling point increases and solubility in water decreases with molecular mass.

   Two consecutive members of the alcohol series (functional group $-\text{OH}$): ${\text{CH}}_3\text{OH}$ (methanol) and ${\text{C}}_2{\text{H}}_5\text{OH}$ (ethanol), which differ by one $-{\text{CH}}_2-$ unit. Any neighbouring pair, such as ${\text{C}}_2{\text{H}}_5\text{OH}$ and ${\text{C}}_3{\text{H}}_7\text{OH}$, is equally correct. (i) The boiling point increases as the molecular mass increases. (ii) The solubility in water decreases as the molecular mass increases.

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7. Q267 CBSE 2022
   Consider the carbon compounds having following molecular ​formula :

   1. (i)${\text{C}}_3{\text{H}}_6$
   2. (ii)${\text{C}}_3{\text{H}}_8$
   3. (iii)${\text{C}}_4{\text{H}}_6$
   4. (iv)${\text{C}}_6{\text{H}}_6$
   5. (v)${\text{C}}_6{\text{H}}_{12}$ (a) State the number of ​double covalent bonds present in ${\text{C}}_3{\text{H}}_6$. (b) Write the formula of first member of the homologous series to which the carbon compound ${\text{C}}_4{\text{H}}_6$ ​belongs. (c) ​Which one of the above compounds forms ring structure of carbon atoms ? (d) Identify, which of ​the above compounds, is ​a ​member of alkane series.
   Show answer

   ${\text{C}}_3{\text{H}}_6$ has one double bond; the first alkyne is ${\text{C}}_2{\text{H}}_2$; ${\text{C}}_6{\text{H}}_6$ has a ring; ${\text{C}}_3{\text{H}}_8$ is an alkane.

   (a) ${\text{C}}_3{\text{H}}_6$ is propene, ${\text{CH}}_2=\text{CH}-{\text{CH}}_3$: it has one double covalent bond, between two of its carbon atoms. (b) ${\text{C}}_4{\text{H}}_6$ fits ${\text{C}}_n{\text{H}}_{2n-2}$, so it belongs to the alkyne series (it is butyne); the first member of this series is ethyne, ${\text{C}}_2{\text{H}}_2$ ($\text{HC}\equiv \text{CH}$). (c) ${\text{C}}_6{\text{H}}_6$ (benzene): its six carbon atoms are joined in a ring. (d) ${\text{C}}_3{\text{H}}_8$ (propane), which fits ${\text{C}}_n{\text{H}}_{2n+2}$ with $n=3$, is the member of the alkane series.

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8. Q268 CBSE 2022
   Consider ​the following organic ​compounds :

   1. (a)Name the functional group ​present in these ​compounds.
   2. (b)Write the ​general formula of ​the compounds ​having this functional group.

   Show answer

   Both compounds contain the carboxylic acid group, $-\text{COOH}$; the general formula is ${\text{C}}_n{\text{H}}_{2n+1}\text{COOH}$.

   (a) Both compounds contain the carboxylic acid (carboxyl) group, $-\text{COOH}$. I is ethanoic acid, ${\text{CH}}_3\text{COOH}$, and II is propanoic acid, ${\text{CH}}_3{\text{CH}}_2\text{COOH}$. (b) The general formula is ${\text{C}}_n{\text{H}}_{2n+1}\text{COOH}$ (also written $\text{R}-\text{COOH}$), where $n=0,1,2,\dots$; I has $n=1$ and II has $n=2$.

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9. Q269 CBSE 2022
   1. (i)What is a Homologous Series ? Write the general formula ​of the homologous ​series for the compounds ​having functional group $-\text{OH}$ and give the ​molecular ​formula for ​the third member ​of this series.
   2. (ii)Draw the ​structure of ethane and write the number of single bonds present in its molecule.
   Show answer

   A homologous series has the same functional group and general formula; alcohols are ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$ and ethane has 7 single bonds.

   (i) A homologous series is a series of carbon compounds that have the same functional group and can be represented by one general formula; successive members differ by a $-{\text{CH}}_2-$ unit ($14$ u in molecular mass), show similar chemical properties and show a gradual change in physical properties. For the compounds with the $-\text{OH}$ functional group (the alcohols) the general formula is ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$. The third member ($n=3$) is propanol, ${\text{C}}_3{\text{H}}_7\text{OH}$, whose molecular formula is ${\text{C}}_3{\text{H}}_8\text{O}$. (ii) Ethane, ${\text{C}}_2{\text{H}}_6$, has the structure ${\text{H}}_3\text{C}-{\text{CH}}_3$: two carbon atoms joined by a single bond, each also bonded to three hydrogen atoms (drawn in full in the figure). A molecule of ethane has $7$ single bonds: $6$ C–H bonds and $1$ C–C bond.

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10. Q270 CBSE 2022
    1. (i)What are Structural Isomers ​? Draw ​the ​structures of ​two ​isomers ​of butane $({\text{C}}_4{\text{H}}_{10})$.
    2. (ii)Write ​the molecular formula of (i) cyclohexane, ​and (ii) benzene.
    Show answer

    Structural isomers have the same formula but different structures: n-butane and isobutane; cyclohexane is ${\text{C}}_6{\text{H}}_{12}$ and benzene is ${\text{C}}_6{\text{H}}_6$.

    (i) Compounds that have the same molecular formula but different structures are called structural isomers. Butane, ${\text{C}}_4{\text{H}}_{10}$, has two: the straight-chain butane (n-butane), ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$, and the branched-chain isobutane (2-methylpropane), ${\text{CH}}_3-\text{CH}({\text{CH}}_3)-{\text{CH}}_3$; both are drawn in full, with every hydrogen, in the figure. (ii) Cyclohexane: ${\text{C}}_6{\text{H}}_{12}$; benzene: ${\text{C}}_6{\text{H}}_6$.

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11. Q271 CBSE 2022
    Draw two different possible structures of a ​saturated hydrocarbon having four ​carbon atoms in its molecule. What are these two structures of the hydrocarbon having same molecular formula called ? Write the ​molecular ​formula and ​the common name of ​this compound. Also write the molecular formula of ​its alkyne.
    Show answer

    The two structures are n-butane and isobutane, called structural isomers; the compound is butane, ${\text{C}}_4{\text{H}}_{10}$, and its alkyne is ${\text{C}}_4{\text{H}}_6$.

    Two structures (both drawn with every bond in the figure): (1) Straight chain, n-butane: ${\text{CH}}_3{\text{–CH}}_2{\text{–CH}}_2{\text{–CH}}_3$ (2) Branched chain, isobutane: ${\text{CH}}_3{\text{–CH(CH}}_3{\text{)–CH}}_3$ Structures of the same molecular formula like these are called structural isomers (isomers). Molecular formula ${\text{C}}_4{\text{H}}_{10}$; common name butane. Its alkyne, butyne, has the molecular formula ${\text{C}}_4{\text{H}}_6$.

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12. Q272 CBSE 2022
    Consider ​the following organic compounds :

    1. (a)Name the functional group present in ​their compounds.
    2. (b)Write ​the ​general formula for the compounds of this functional group.
    3. (c)State the ​relationship between these compounds and ​draw ​the ​structure of any other compound having similar functional group.

    Show answer

    Both compounds have the aldehyde group $-\text{CHO}$, general formula ${\text{C}}_n{\text{H}}_{2n}\text{O}$; they are homologues, and another member is methanal.

    (a) The aldehyde group, $-\text{CHO}$: a carbon at the end of the chain, double-bonded to oxygen and bonded to hydrogen. Compound (i) is propanal, ${\text{CH}}_3{\text{CH}}_2\text{CHO}$, and (ii) is ethanal, ${\text{CH}}_3\text{CHO}$. (b) ${\text{C}}_n{\text{H}}_{2n}\text{O}$ (also written $\text{R}-\text{CHO}$) for aldehydes with a saturated chain. (c) They are members of the same homologous series (homologues): they have the same functional group and differ by one ${\text{CH}}_2$ unit, that is by $14$ u in molecular mass ($58$ u and $44$ u). Another compound with the same group is methanal, $\text{HCHO}$, drawn as a carbon atom bonded to two hydrogen atoms and joined to an oxygen atom by a double bond (butanal, ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{CHO}$, is equally acceptable).

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13. Q273 CBSE 2022
    State the reason why

    1. (i)carbon compounds have low melting ​and ​boiling points.
    2. (ii)carbon compounds ​do not conduct ​electricity.
    3. (iii)​carbon can form only ​covalent ​compounds.
    Show answer

    Weak forces between molecules give low melting points, no ions means no conduction, and carbon shares its four valence electrons to form covalent bonds.

    (i) Carbon compounds are covalent compounds made up of separate molecules, and the forces of attraction between these molecules are weak. Little heat energy is needed to separate the molecules, so the melting and boiling points are low. (ii) The atoms in carbon compounds are held together by shared pairs of electrons, so no ions (charged particles) are formed and there are no free electrons. With nothing to carry charge, carbon compounds do not conduct electricity; they are generally poor conductors. (iii) Carbon has four valence electrons (configuration 2, 4). To gain four electrons and form ${\text{C}}^{4-}$, a nucleus of six protons would have to hold ten electrons, which is difficult; to lose four electrons and form ${\text{C}}^{4+}$ would need a large amount of energy. So carbon shares its four valence electrons with other atoms and forms covalent bonds.

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14. Q274 CBSE 2022
    1. (i)In the given below compound identify ​(I) the heteroatom, and (II) ​the functional group.
    2. (ii)Write the structural formula ​of butane (${\text{C}}_4{\text{H}}_{10}$).
    3. (iii)Draw the complete ​structure of the molecule of (I) Cyclohexane, and (II) Benzene. Which of the two is ​unsaturated ?

    Show answer

    The heteroatom is oxygen and the functional group is $-\text{OH}$; butane is a four-carbon chain; benzene is the unsaturated one.

    (i) (I) The heteroatom is oxygen, O. (II) The functional group is $-\text{OH}$, the alcohol group; the compound is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$. (ii) Butane is ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$: four carbon atoms in a chain joined by single bonds, the two end carbons carrying three hydrogens each and the two middle carbons two each (drawn in full in the figure). (iii) (I) Cyclohexane, ${\text{C}}_6{\text{H}}_{12}$: a ring of six carbon atoms joined by single bonds, each carbon bonded to two hydrogens. (II) Benzene, ${\text{C}}_6{\text{H}}_6$: a ring of six carbon atoms, each bonded to one hydrogen, with alternate single and double bonds. Benzene is the unsaturated one.

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15. Q275 CBSE 2022
    What are structural ​isomers ​? ​Draw the structure of two ​isomers of butane ${\text{C}}_4{\text{H}}_{10}$. Explain with ​the help of structure why we ​cannot have isomers ​of ​propane.
    Show answer

    Structural isomers have the same molecular formula but different structures; butane has two, but propane's three carbons can join in only one way.

    Structural isomers are compounds that have the same molecular formula but different structures, that is, different arrangements of their atoms. Two isomers of butane, ${\text{C}}_4{\text{H}}_{10}$ (structures drawn in the figure): (1) butane (n-butane), the straight chain ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$; (2) 2-methylpropane (isobutane), the branched chain ${\text{CH}}_3-\text{CH}({\text{CH}}_3)-{\text{CH}}_3$. Propane, ${\text{C}}_3{\text{H}}_8$ (${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_3$), has no isomers because its three carbon atoms can be joined in only one way, as the chain C–C–C. Attaching the third carbon to the middle carbon gives the same chain drawn with a bend, and a branch needs a carbon joined to three other carbons, which requires at least four carbon atoms.

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16. Q276 CBSE 2022
    1. (i)​Write ​the ​molecular formula of benzene and draw its structure.
    2. (ii)Write the ​number of single and double covalent bonds present in a molecule ​of benzene.
    3. (iii)Which compounds ​are called alkynes ?
    Show answer

    Benzene is ${\text{C}}_6{\text{H}}_6$ with 9 single and 3 double bonds; alkynes are hydrocarbons with a carbon-carbon triple bond.

    (i) Molecular formula of benzene: ${\text{C}}_6{\text{H}}_6$. Structure: six carbon atoms in a hexagonal ring joined by alternate single and double bonds, with one hydrogen atom bonded to each carbon (drawn in the figure). (ii) Single covalent bonds: $9$ (three C–C and six C–H). Double covalent bonds: $3$ (all C=C). (iii) Hydrocarbons that contain a triple bond between two carbon atoms are called alkynes; with one triple bond their general formula is ${\text{C}}_n{\text{H}}_{2n-2}$, for example ethyne, $\text{H–C}\equiv \text{C–H}$ (${\text{C}}_2{\text{H}}_2$).

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17. Q277 CBSE 2022
    1. (a)Draw the electron dot ​structure for ethyne.
    2. (b)List two ​differences ​between the properties exhibited by covalent ​compounds ​and ionic compounds.
    Show answer

    In ethyne the carbons share three pairs of electrons; covalent compounds have low melting points and are poor conductors, unlike ionic compounds.

    (a) Ethyne, ${\text{C}}_2{\text{H}}_2$ ($\text{H}-\text{C}\equiv \text{C}-\text{H}$): each hydrogen shares one pair of electrons with a carbon, and the two carbons share three pairs, a triple bond — five shared pairs, ten electrons, as drawn in the figure. Each carbon then has an octet ($2+6=8$ electrons) and each hydrogen a duplet ($2$ electrons). (b) Any two of: (1) Covalent compounds generally have low melting and boiling points, whereas ionic compounds have high melting and boiling points. (2) Covalent compounds are generally poor conductors of electricity, whereas ionic compounds conduct electricity in the molten state or in aqueous solution. (3) Ionic compounds are generally soluble in water and insoluble in solvents such as kerosene and petrol, whereas many covalent compounds do not dissolve in water but dissolve in such organic solvents.

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18. Q278 CBSE 2022
    What ​is a homologous series ? ​Find the difference in molecular mass between ​the two consecutive members of a ​homologous ​series. ​State how in a homologous series of carbon compounds the following properties vary with increase in ​molecular mass :

    1. (i)Melting and boiling points
    2. (ii)Chemical properties
    Show answer

    Consecutive members differ by ${\text{CH}}_2$, a mass difference of 14 u; melting and boiling points rise with molecular mass while chemical properties stay similar.

    A homologous series is a series of carbon compounds that have the same functional group, in which successive members differ by a $-{\text{CH}}_2-$ unit; the members share a general formula and have similar chemical properties (for example ${\text{CH}}_3\text{OH}$, ${\text{C}}_2{\text{H}}_5\text{OH}$, ${\text{C}}_3{\text{H}}_7\text{OH}$). Difference in molecular mass between two consecutive members $=12+2\times 1=14$ u. (i) The melting and boiling points increase as the molecular mass increases: the physical properties show a gradation (steadily for the boiling points, as a broad trend for the melting points). (ii) The chemical properties remain similar, because they are decided by the functional group, which is the same in every member.

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19. Q279 CBSE 2022
    1. (i)A ​compound with molecular formula ${\text{C}}_3{\text{H}}_6\text{O}$ has ​two isomers. (I) Draw the ​structures of both the isomers. (II) Write ​their functional group.
    2. (ii)Why are ​the ​compounds of carbon exceptionally ​stable ?
    Show answer

    Propanal and propanone have the aldehyde and ketone groups; carbon compounds are stable because the small carbon atom forms strong bonds.

    (i)(I) Propanal, ${\text{CH}}_3-{\text{CH}}_2-\text{CHO}$, and propanone (acetone), ${\text{CH}}_3-\text{CO}-{\text{CH}}_3$, drawn in full in the figure. (II) Propanal has the aldehyde group, $-\text{CHO}$; propanone has the ketone group, $>\text{C}=\text{O}$. (ii) Carbon is a small atom, so its nucleus holds the shared pairs of electrons strongly. The bonds carbon forms with most other elements, and with other carbon atoms, are therefore very strong, and this makes carbon compounds exceptionally stable.

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20. Q280 CBSE 2022
    What is a ​homologous series of carbon compounds ? Write ​the general ​formula of

    1. (i)alcohols, and
    2. (ii)aldehydes. Draw ​the structure of the first member ​of ​each series.
    Show answer

    A homologous series has a common functional group and general formula; alcohols are ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$, aldehydes ${\text{C}}_n{\text{H}}_{2n+1}\text{CHO}$; first members are methanol and methanal.

    A homologous series is a series of carbon compounds in which the same functional group substitutes for hydrogen in a carbon chain. Successive members differ by a $-{\text{CH}}_2-$ unit ($14$ u), have similar chemical properties and show a gradual change in physical properties, and the series can be represented by one general formula. (i) Alcohols: ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$ ($n=1,2,3,\dots$). (ii) Aldehydes: ${\text{C}}_n{\text{H}}_{2n+1}\text{CHO}$ ($n=0,1,2,\dots$), which is the same as ${\text{C}}_m{\text{H}}_{2m}\text{O}$ ($m=1,2,3,\dots$) when every carbon atom is counted. First members (structures drawn in the figure): methanol, ${\text{CH}}_3\text{OH}$, in which one carbon atom is bonded to three hydrogen atoms and an $-\text{OH}$ group; and methanal (formaldehyde), $\text{HCHO}$, in which one carbon atom is bonded to two hydrogen atoms and double-bonded to an oxygen atom.

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