CBSE Class 10 Science 2026 — Paper 31/3/1

UNEP's 1987 Montreal Protocol froze CFC production at 1986 levels; ozone shields the Earth from harmful UV radiation.

Aerobic respiration gives more energy because it breaks glucose down completely with oxygen, whereas anaerobic respiration breaks it down only partially.

The blanks are 2-chambered, amphibians and reptiles, and double circulation, which is also the most efficient as it keeps oxygenated and deoxygenated blood apart.

Vessels and tracheids joined end to end form a continuous column of water, moved up by root pressure and transpiration pull.

The cross $TT\times tt$ gives all-tall $Tt$ plants in ${\text{F}}_1$; tallness is dominant, shortness is recessive, and the traits do not blend.

Transpiration is minimised because the stomata stay closed by day; gas exchange in photosynthesis takes place through the stomata.

Photosynthesis: light absorbed, water split, carbon dioxide reduced; desert plants take in carbon dioxide at night; stomata have guard cells around the pore.

Bryophyllum leaf buds show vegetative propagation; asexual reproduction gives identical offspring, whereas sexual reproduction gives variation that helps survival and evolution.

Multiple fission (asexual) occurs in Plasmodium; vegetative propagation raises plants that cannot make seeds, giving earlier flowering and genetically similar plants.

Two Na atoms give one electron each to O, forming ${\text{Na}}_2\text{O}$; Mg gives one electron to each of two Cl atoms, forming ${\text{MgCl}}_2$.

It is a thermal decomposition, $2{\text{FeSO}}_4\stackrel{\text{heat}}{\to }{\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$, and it is endothermic because heat must be absorbed continuously.

Mixing acid with water is highly exothermic; ${\text{H}}^{+}$ ions form only in water; heating removes the water of crystallisation that makes copper sulphate blue.

Electrolysis of brine gives sodium hydroxide; brine with ammonia and carbon dioxide gives baking soda; heating gypsum at 373 K gives Plaster of Paris.

Anode mud settles below the anode; the anode is impure copper and the cathode pure copper; heating copper sulphide in air gives copper.

${\text{C}}_2{\text{H}}_4$ and ${\text{C}}_4{\text{H}}_8$ are in one series; products are ethyl ethanoate with water, and carbon dioxide with water; soap tails cluster inward, forming micelles.

Propanone and propyne; hydrogenation; ${\text{C}}_4{\text{H}}_{10}$ has the higher molecular mass; sodium gives hydrogen and sodium ethoxide; the ester gives sodium ethanoate and ethanol.

Medium A is optically denser because the ray bends away from the normal; $n_{BA}=\frac{V_A}{V_B}$.

Very fine particles scatter mainly blue light; very large particles scatter all wavelengths almost equally, so the light appears white.

A rainbow forms when raindrops disperse sunlight by refraction, internal reflection and refraction, giving a spectrum with red outside and violet inside.

The defect is hypermetropia: the image forms behind the retina; a convex lens corrects it.

A cell or battery keeps the potential difference constant, a rheostat changes the current, and the heater draws $10$ A at 220 V.

Total resistance is $5\Omega$, the battery supplies $2$ A, and the potential difference between P and Q is $5$ V.

$f=25$ cm; observation 6 is incorrect because $v$ must be negative; $m=-5$, so the image is real, inverted and magnified.

A solenoid's field is uniform inside and like a bar magnet's outside; a stretched solenoid gives concentric circular field lines.

A current-carrying rod in a field is pushed sideways; the electron's force is into the paper and unchanged if field and motion both reverse.