CBSE Class 10 Science 2025 — Paper 31/2/1

It is a displacement reaction, $\text{Cu}+2{\text{AgNO}}_3\to {\text{Cu(NO}}_3{)}_2+2\text{Ag}$; silver is refined by electrolytic refining.

Structures (1) and (4) are aldehydes of one homologous series; with rising molecular mass the melting point increases and solubility decreases.

The hind-brain has the cerebellum, pons and medulla; the medulla controls involuntary actions such as blood pressure and salivation.

The seed coat protects the embryo, the cotyledon stores food, the radicle forms the root and the plumule forms the shoot.

Dissolve sugar in water, add yeast, keep it warm for one to two hours, then observe a drop under a microscope.

A concave lens diverges a parallel beam; the refracted rays appear to come from its virtual principal focus $F$.

A ray passing through the principal focus emerges parallel to the axis after a convex lens; the point is the principal focus.

No; the kettle draws about 3.41 A, more than the 3 A rating, so the fuse would melt.

A decomposition reaction breaks one reactant into simpler products; composting releases heat to the surroundings, so it is exothermic.

Decomposition reverses combination: calcium oxide and water combine to give calcium hydroxide, whereas calcium carbonate breaks into calcium oxide and carbon dioxide.

Two Na atoms each give one electron to an O atom, forming two ${\text{Na}}^{+}$ cations and one ${\text{O}}^{2-}$ anion in ${\text{Na}}_2\text{O}$.

A hormone is a chemical messenger from a ductless gland; feedback keeps its quantity precise, as falling blood glucose reduces insulin secretion.

The father is $ff$ and the mother $Ff$; the progeny are $Ff$ (free earlobe) and $ff$ (attached earlobe) in the ratio $1:1$.

Virtual, erect and enlarged image at $v=-24$ cm on the object's side; focal length $f=+8$ cm.

In series the equivalent resistance is $11\Omega$; in parallel it is $1\Omega$.

Ozone absorbs harmful UV radiation; it forms when UV splits ${\text{O}}_2$ and the atoms combine with ${\text{O}}_2$; CFCs deplete it.

'X' is ethanoic acid, a weaker acid than HCl; it forms esters with alcohols and sodium ethanoate with sodium carbonate.

Saturated hydrocarbons have only single bonds, unsaturated ones a double or triple bond; nickel hydrogenation makes vanaspati ghee; the four-carbon alkene is but-1-ene.

Herbivores need a longer small intestine; bile makes food alkaline and emulsifies fat, pancreatic enzymes digest the food, and villi absorb it.

Cartilage rings keep the trachea open; the diaphragm and ribs enlarge the chest so air rushes in; oxygen shortage makes lactic acid, causing cramps.

Field lines are clockwise circles (seen from above) by the right-hand thumb rule; the force on the electron is out of the paper.

A solenoid is a closely wound coil with a bar-magnet-like field, uniform inside; a soft iron core inside it, with current, makes an electromagnet.

P is near pH 0 and Q near pH 14; the hydronium ion concentration becomes 100 times greater, turning pH paper orange to red.

Fertilisation occurs in the oviduct; the uterine lining thickens for implantation; an unfertilised egg leads to menstruation; the placenta nourishes the embryo.

Dispersion; each colour has a different refractive index and bends differently; an inverted second prism recombines the colours; raindrops disperse sunlight into a rainbow.