CBSE Class 10 Science 2026 — Paper 31/2/1

Feedback mechanisms regulate hormone release; for example, rising blood sugar makes the pancreas release more insulin and falling sugar reduces it.

Impulses reach only cells connected by nervous tissue, and a cell needs time to reset before it can generate a new impulse.

Variation lets some individuals survive a drastic change in their surroundings, so the species does not die out.

Compost kitchen waste, recycle or reuse metal and plastic bottles, and incinerate sanitary waste.

A is cytoplasm, B ethanol, C carbon dioxide, D lactic acid, E carbon dioxide and F water.

Sex can be set by egg temperature (turtles) or by changing sex (snails); females have $XX$ and males $XY$ sex chromosomes.

Voluntary actions are done by will; the cerebellum gives precision; the medulla controls involuntary actions; muscle proteins change shape and the muscle contracts.

The testes need a temperature below body temperature; sperms travel testis, vas deferens, urethra, vagina, uterus and oviduct, helped by the long tail.

Radha can use oral pills or condoms; the surgical methods are vasectomy and tubectomy; gonorrhoea is a bacterial and HIV-AIDS a viral STD.

Test tube B, because iron is more reactive than copper and displaces it from copper sulphate: $\text{Fe}+{\text{CuSO}}_4\to {\text{FeSO}}_4+\text{Cu}$.

Sodium is soft enough to cut and graphite conducts; Mg gives two electrons to O, forming ionic $\text{MgO}$.

Oxides are easier to reduce; aluminium oxide reacts with both acids and bases; Na, K, Ca and Mg are too reactive to occur free.

Copper turns black as copper(II) oxide on heating; hydrogen reduces it back to reddish-brown copper and colourless water.

X is chlorine, Y hydrogen, Z sodium hydroxide; red litmus turns blue; ${\text{CO}}_2$ with ammoniacal brine gives baking soda; A is bleaching powder.

P is ethanol; heated with conc. sulphuric acid at 443 K it dehydrates to ethene (Q); with ethanoic acid it forms a sweet-smelling ester.

Benzene is a hexagonal ring of six carbons; carbon forms covalent bonds; ethanol is oxidised to ethanoic acid; the ester gives sodium ethanoate and ethanol.

The refractive index of Medium 2 with respect to Medium 1 is $n_{21}=\sqrt{3}=1.732$.

The focal length of the eye lens decreases for nearer objects and increases for farther ones, so the image stays on the retina.

A concave lens makes rays from a distant object appear to come from the far point, so the eye focuses them on the retina.

$m=v/u$; the image is 8 cm tall, virtual and erect, 20 cm from the lens on the object's side.

Scattering sends light in all directions from tiny particles in its path; reflection turns it back from a surface in one direction.

The graph is a straight line through the origin; its slope gives the resistance $R=3\Omega$.

The fridge warms the kitchen air by the heating effect of current, $H=I^{2}Rt$; irons and bulbs use it; or $1\text{kWh}=3.6\times 10^6$ J.

Fleming's left-hand rule gives the force; a fuse protects the circuit; the earth pin prevents shock; the force on AB is into the paper.

Right-hand thumb rule gives the field direction; only an identical fuse rating protects the circuit; soft iron makes the electromagnet strong yet temporary.