Class 10 Science · Chapter 3

Metals and Non-metals

344 Class 10 Science questions on Metals and Non-metals 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 18 of 18

1. Q341 CBSE 2017
   The ​atomic number of an element is ​12.

   1. (a)​Write ​its electronic configuration and determine ​its ​valency.
   2. (b)Is it more reactive or less reactive than Ca (atomic number 20) ? Justify your answer giving ​reason.
   3. (c)Is it a metal or a non-metal ?
   4. (d)Write the ​formula of its oxide.
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   The element is magnesium ($2,8,2$): valency 2, less reactive than calcium, a metal, with oxide $\text{MgO}$.

   (a) Electronic configuration: 2, 8, 2 (K = 2, L = 8, M = 2). The atom has 2 valence electrons, which it loses, so its valency is 2. (The element is magnesium, Mg.) (b) It is less reactive than calcium. Calcium ($Z=20$) has the configuration 2, 8, 8, 2: both elements have 2 valence electrons and are in group 2, with calcium below magnesium. Calcium's atom has one more shell, so its valence electrons are farther from the nucleus and held less strongly; calcium loses them more easily and is therefore more reactive. (c) It is a metal: it loses its 2 valence electrons to form a positive ion, ${\text{Mg}}^{2+}$. (d) The formula of its oxide is $\text{MgO}$.

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2. Q342 CBSE 2017
   Write the electronic configuration of two elements X and Y whose atomic ​numbers are ​20 and ​17 respectively. ​Write the molecular formula of the compound ​formed when element X reacts with ​element Y. Draw electron-dot ​structure of the product and also state the ​nature of the bond formed between both the elements.
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   X ($2,8,8,2$) and Y ($2,8,7$) form the ionic compound ${\text{XY}}_2$, ${\text{CaCl}}_2$, by transfer of electrons.

   Electronic configurations: X (atomic number 20) is $2,8,8,2$ (calcium); Y (atomic number 17) is $2,8,7$ (chlorine). Formula of the compound: ${\text{XY}}_2$, that is, ${\text{CaCl}}_2$ (X loses 2 electrons; each Y gains 1). Electron-dot structure: calcium transfers one electron to each of two chlorine atoms, forming ${\text{Ca}}^{2+}$ and two ${\text{Cl}}^{-}$ ions, each chloride with eight electrons in its outer shell (see the figure). Nature of the bond: ionic (electrovalent) bond, formed by the transfer of electrons from X to Y.

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3. Q343 CBSE 2017
   An element ​‘M’ ​has atomic ​number 12.

   1. (i)Write ​its electronic ​configuration ​and valency.
   2. (ii)Is ‘M’ a metal or a non-metal ? Give reason in support of your answer.
   3. (iii)Write the formula and nature (acidic / basic) of ​the oxide ​of M.
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   M ($2,8,2$) has valency 2, is a metal because it loses two electrons, and forms the basic oxide $\text{MO}$.

   (i) Electronic configuration of M: $2,8,2$. M loses its two valence electrons to attain the configuration of neon, so its valency is $2$. (ii) M is a metal. Its atom has only two electrons in its outermost shell, which it loses easily to form a positive ion, ${\text{M}}^{2+}$; losing electrons to form positive ions is characteristic of metals. (M is magnesium, in Group 2.) (iii) Formula of the oxide: MO (magnesium oxide, $\text{MgO}$). Nature: basic — it dissolves in water to form magnesium hydroxide, $\text{MgO}+{\text{H}}_2\text{O}\to {\text{Mg(OH)}}_2$, which turns red litmus blue.

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4. Q344 CBSE 2017
   An element ‘X’ with electronic configuration (2, 8, 2) combines separately with ​two radicals, $({\text{NO}}_3{)}^{-}$ and $({\text{SO}}_4{)}^{2-}$.

   1. (i)Is ‘X’ a ​metal ​or a non-metal ? Write the nature of its oxide.
   2. (ii)​Write the formula of the compounds of ‘X’ formed by the combination of these ​radicals. Are ​these compounds covalent ​or electrovalent ?
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   X is a metal with a basic oxide; its compounds ${\text{X(NO}}_3{)}_2$ and ${\text{XSO}}_4$ are electrovalent.

   (i) X is a metal: its atom has only two electrons in the outermost shell and gives them up to form the ion ${\text{X}}^{2+}$ (with 12 electrons in all, X is magnesium). Its oxide, XO, is basic. (ii) With the nitrate radical X forms ${\text{X(NO}}_3{)}_2$, and with the sulphate radical it forms ${\text{XSO}}_4$. Both are electrovalent (ionic) compounds, made of ${\text{X}}^{2+}$ ions and negatively charged radicals held together by electrostatic attraction.

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