CBSE Class 10 Science 2025 — Paper 31/5/1

X is ferrous sulphate crystals and Y is ferric oxide; the colour changes from green to white and then reddish brown.

The testes hang outside the body because sperm formation needs a lower temperature; the glands' secretions carry and nourish the sperms.

Plasma and proteins leak from capillaries into tissue spaces as lymph, which carries absorbed fat and drains excess fluid back into the blood.

X is the Bowman's capsule, which collects the initial filtrate; useful substances are reabsorbed selectively because the body still needs them.

Kerosene is optically denser but less dense in mass than water, and light is slower in it, so the two densities are independent.

Joule heating is used in heating appliances and the electric fuse; $1\text{kW h}=3.6\times 10^6\text{J}$.

Joule heating is used in heating appliances and in the fuse; the parallel combination has $R_p=1.09\Omega$.

Producers capture the Sun's energy for all other organisms; energy enters once, moves one way and is lost as heat: unidirectional.

Washing soda is ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$, made by heating baking soda and recrystallising the sodium carbonate formed.

M is iron; it rusts in tube A but not in B (oil) or C (dry air), so rusting needs both air and moisture.

Al gives three electrons to N to form ${\text{Al}}^{3+}$ and ${\text{N}}^{3-}$, giving AlN; ionic solids are brittle because like charges repel when layers slip.

Haemoglobin carries oxygen; residual air keeps alveoli open and allows time for exchange; ATP stores and releases energy for all cell activities.

Fertilisation is the fusion of male gamete and egg; afterwards the zygote becomes the embryo, ovule the seed and ovary the fruit.

Concave lens, $f=-4$ m; used for myopia; the image is virtual, erect and diminished, between $F$ and $O$.

The length of the wire is $5\times 10^{-3}$ m, that is 0.005 m.

The earth wire carries leaking current safely to the ground, preventing shock; avoid overloading by not crowding sockets or circuits.

A homologous series has one functional group and members differing by $-{\text{CH}}_2-$; ethanoic acid gives sodium ethanoate with NaOH and ethyl ethanoate with ethanol.

Ethyne is ${\text{C}}_2{\text{H}}_2$ with a triple bond; ethanol gives sodium ethoxide with sodium, an ester with ethanoic acid and ethanoic acid with dichromate.

Iodine deficiency causes goitre, too little growth hormone causes dwarfism, testosterone brings facial hair; hormones reach every cell and give a steady signal.

Voluntary actions are controlled by the cerebrum, involuntary ones by the mid-brain and medulla; a reflex action is processed by the spinal cord.

Light is fastest in C ($v_A=v_B$ less than $v_C$); A and B are equally dense and C is the rarest.

(a) $f=+20$ cm; (b) $m=-2$; (c) observation 1 gives a virtual, erect image, observation 2 a real, inverted one.

Element A gains two electrons (${\text{A}}^{2-}$); butene has 10 single and 1 double bond; ammonia has three shared pairs and a lone pair.

Chromosomes carry genes; the male XY pair is mismatched; boys and girls are $50:50$; turtles and snails show non-genetic sex.

Lines emerge from N and merge at S; closer lines mean a stronger field; lines never cross; the field inside a solenoid is uniform.