Q&A: practice questions with answers

Concept: Average velocity = net displacement ÷ total time.

1. Displacement A → C = $1000-500=500$ m.
2. Total time = $100+100=200$ s.
3. Average velocity = $\frac{500}{200}=2.5$ m/s.
4. Speed changes (10 → 5 m/s) and direction reverses → non-uniform motion.

Trick: 0.4 is a trap ($\frac{200}{500}$ inverted); a turning body can never be in uniform motion.

Answer: (C) 2.5 m/s and Non-Uniform Motion

Concept: Each epithelium type matches a function (NCERT Class 9).

1. Columnar epithelium → absorption and secretion (intestine lining).
2. Cuboidal epithelium → mechanical support (kidney tubules, salivary gland ducts).
3. Ciliated → pushing mucus; squamous → delicate lining; stratified → preventing wear and tear.

Yaad rakhein: Cube = box = strong → 'support'; Column = tall cells → 'absorb'.

Answer: (A) Mechanical support

Concept: Lysosomes contain powerful digestive enzymes.

1. When a cell is damaged, lysosomes burst and their enzymes digest the cell itself.
2. Hence they are called 'suicide bags' of the cell.
3. Nucleus = control centre, mitochondria = powerhouse, ribosomes = protein factories.

Yaad rakhein: Lysosomes also act as the cell's waste-disposal system.

Answer: (C) Suicidal bags of the cell

Concept: Average speed = total distance ÷ total time.

1. Total distance = $16+16=32$ m.
2. Total time = $4+2=6$ s.
3. Average speed = $\frac{32}{6}\approx 5.33$ m/s.

Trick: Don't average the speeds (4 and 8 → 6 is wrong); for equal distances use $\frac{2ab}{a+b}=\frac{2\times 4\times 8}{12}=5.33$.

Answer: (A) 5.33 m/s

Concept: After ovulation the egg can be fertilised only for a short time.

1. An unfertilised ovum survives for about one day (12–24 hours).
2. If not fertilised, it degenerates and the uterine lining is later shed as menstruation.

Yaad rakhein: The ovary releases one egg roughly every month — 'one month' is the cycle, not the egg's life.

Answer: (A) About one day

Concept: $F=m\times a$.

1. Unit = $\text{kg}\times {\text{m/s}}^2={\text{kg m/s}}^2$ = 1 newton (N).
2. N m (= joule) is unit of work/torque; kg m/s is unit of momentum.

Trick: Write the formula's units: mass (kg) × acceleration (m/s²).

Answer: (C) kg m/s²

Concept: Molecular formula = n × empirical formula, n = molar mass ÷ empirical mass.

1. C : H : O = $\frac{40}{12}:\frac{6.7}{1}:\frac{53.3}{16}$ = 3.33 : 6.7 : 3.33 = 1 : 2 : 1 → CH₂O.
2. Empirical mass = $12+2+16=30$.
3. $n=\frac{60}{30}=2$ → C₂H₄O₂ (acetic acid).

Trick: Just find the option with mass 60: C₂H₄O₂ = $24+4+32=60$.

Answer: (A) C₂H₄O₂

Concept: The embryo attaches to the thick, blood-rich inner wall of the uterus.

1. Fertilisation occurs in the fallopian tube (oviduct).
2. The developing embryo moves down and gets implanted in the uterine lining.
3. Placenta then forms there for nutrition.

Yaad rakhein: Fertilisation → oviduct; implantation → uterus wall.

Answer: (A) Lining of the uterus

Concept: $W=F\times s\times \cos \theta$.

1. Force and displacement in same direction → $\theta =0^{\circ }$, $\cos 0^{\circ }=1$.
2. $W=5\times 50=+250$ J.

Trick: Same direction → work is positive; this alone removes both negative options.

Answer: (D) + 250 J

Concept: Sexual reproduction combines DNA of two parents.

1. Gametes from two different individuals fuse → new combinations of genes.
2. This creates variation, which helps populations survive changing environments.
3. Asexual reproduction copies DNA almost exactly → little variation.

Yaad rakhein: Variation is the raw material for evolution.

Answer: (D) It mixes DNA from two parents to create new variations.

Concept: $\text{pH}=-\log [{\text{H}}^{+}]$; HCl is a strong acid and ionises completely.

1. $[{\text{H}}^{+}]=0.01\text{M}={10}^{-2}\text{M}$.
2. $\text{pH}=-\log ({10}^{-2})=2$.

Trick: For ${10}^{-n}$ M strong monobasic acid, $\text{pH}=n$. Acid → pH must be below 7, so 8 and 12 are out at once.

Answer: (C) 2

Concept: Lysosomes hold hydrolytic (digestive) enzymes.

1. These enzymes break down proteins, lipids, carbohydrates and nucleic acids, and worn-out organelles.
2. Protein synthesis = ribosomes; membrane transport = plasma membrane; genetic material = nucleus.

Yaad rakhein: Lyso = 'to break/digest' — lysosome = digestive bag of the cell.

Answer: (A) Breaking down proteins, lipids, and carbohydrates

Concept: Storage losses come from living and non-living factors.

1. Biotic: insects, rodents, fungi, mites, bacteria.
2. Abiotic: inappropriate moisture and temperature.

Yaad rakhein: Prevention: dry grains well, clean storage, and fumigation with chemicals.

Answer: (A) Biotic and Abiotic

Concept: Compression is a physical change; it cannot alter the composition of a mixture.

1. Air is a homogeneous mixture of N₂, O₂, Ar, CO₂ etc.
2. Halving the volume only brings molecules closer; the proportion of gases stays the same.
3. No chemical reaction occurs, so no compound forms.

Trick: Options B, C, D all claim a change in composition — only A is consistent with a physical process.

Answer: (A) The composition of air remains same because it is a mixture.

Concept: Impure metal = anode, pure metal = cathode, salt solution of the metal = electrolyte.

1. Electrolyte: acidified copper sulphate solution ✓.
2. Anode = impure Cu, cathode = pure Cu (A and D reversed).
3. Impurities settle below the anode as anode mud, not cathode mud.

Trick: 'Pure goes to cathode' — anything saying pure copper at anode is wrong.

Answer: (B) Electrolyte – Acidified Copper sulphate solution

Concept: Nervous tissue is specialised for receiving and conducting impulses.

1. Statement A: neurons transmit electrical impulses rapidly → correct.
2. Statement B: structural/mechanical support is the job of connective tissue (bone, cartilage) → incorrect.

Yaad rakhein: Neuron = cell body (cyton) + dendrites + axon; it is the longest cell in the body.

Answer: (A) Statement A is correct but B is incorrect.

Concept: $W=m\times g$; mass is the amount of matter, g depends on location.

1. Mass is constant everywhere.
2. g on the Moon ≈ $\frac{1}{6}$ of Earth's → weight changes.
3. Option A is a true fact but doesn't explain why; weight is a vector and mass a scalar (D reversed).

Trick: Choose the option that gives the cause (g varies), not just a related fact.

Answer: (B) Weight depends on the local value of g, which varies with location

Concept: Tall pillar-like cells increase surface for absorption and secretion.

1. Columnar epithelium lines the inner surface of the intestine → absorption.
2. Cuboidal → mechanical support; stratified → protects skin from wear and tear.
3. Ciliated columnar is found in the respiratory tract, not intestine.

Yaad rakhein: Columnar ↔ absorption (intestine) — the same pair appears in analogy questions.

Answer: (A) Columnar epithelium

Concept: In a stethoscope, the heartbeat sound travels along the tube by repeated (multiple) reflections.

1. Assertion: true.
2. Reason: true — sound is a mechanical wave and needs a medium.
3. But the reason does not explain why multiple reflection is used → not the correct explanation.

Trick: Ask 'Assertion because Reason?' — 'stethoscope uses reflection because sound needs a medium' doesn't make sense → option C.

Answer: (C) Both assertion and reason are true and the reason is not the correct explanation of the assertion.

Concept: Rays parallel to the principal axis converge at the principal focus after reflection from a concave mirror.

1. Concave mirror is a converging mirror.
2. All parallel rays meet at one point F on the principal axis.
3. Option A describes a convex mirror (rays appear to diverge from F behind it).

Yaad rakhein: Concave → converge (real F in front); Convex → diverge (virtual F behind).

Answer: (D) They all meet at a single point on the principal axis.