CBSE Class 10 Science 2025 — Paper 31/5/3

It is a convex mirror, with $0<m<1$ and $R=40$ cm.

Maximum resistance is $1\Omega$ (all five in series); minimum is $0.04\Omega$ (all five in parallel).

The potential difference across the resistor is 20 V.

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.

(a) Grass to mouse to eagle and grass to mongoose to eagle (shortest chains); (b) the eagle, by biological magnification.

Copper burns to black copper(II) oxide, $2\text{Cu}+{\text{O}}_2\to 2\text{CuO}$; passing hydrogen over the heated wire reverses it.

Force depends on current, field strength and length in the field; it is maximum at right angles to the field; Fleming's left-hand rule.

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

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

Cross-pollination is better for survival: it brings more variation, so some individuals can survive changed surroundings, unlike self-pollination, which gives similar offspring.

Carbon dioxide from air via stomata, water from soil via roots and xylem, and sunlight from the Sun are the raw materials.

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.

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.

Functional group gives characteristic properties; propanol has $-\text{OH}$, propanone $>\text{C}=\text{O}$; ethanol to ethene is dehydration, ethanol to ethanoic acid is oxidation.

Cyclohexane and benzene are cyclic hydrocarbons; soap molecules cluster in water with tails inward and ionic ends outward, forming micelles that trap oily dirt.

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.

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

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.