Q&A: practice questions with answers

Concept: Food passes through the alimentary canal in a fixed sequence.

1. Mouth: chewing and saliva (starch digestion begins).
2. Oesophagus (food pipe): carries food by peristalsis.
3. Stomach → small intestine → large intestine → anus.

Yaad rakhein: Order: Mouth → Oesophagus → Stomach → Small intestine → Large intestine.

Answer: (B) Mouth - Oesophagus - Stomach

Concept: In uniform motion speed is constant, so distance is proportional to time: $d=v\times t$.

1. $v=\frac{25}{5}=5\text{m/s}$.
2. Distance in 3 s $=5\times 3=15\text{m}$.

Trick: Unitary method: 5 s → 25 m, so 3 s → $\frac{25}{5}\times 3=15\text{m}$.

Answer: (C) 15 m

Concept: A current-carrying solenoid behaves like a bar magnet; inside it the field lines are parallel and the field is strong and uniform.

1. More turns → stronger field: (A) correct.
2. Acts like a bar magnet with N and S ends: (B) correct.
3. Near the centre of a long solenoid field is nearly uniform: (C) correct.
4. Outside, field lines spread out, so the field is weak, not extremely large: (D) is INCORRECT.

Trick: Solenoid: strong & uniform INSIDE, weak OUTSIDE.

Answer: (D) The magnitude of the magnetic field outside but close to the solenoid is extremely large.

Concept: In a double displacement reaction two compounds exchange their ions: $AB+CD\to AD+CB$.

1. $2\mathrm{K}\mathrm{B}\mathrm{r}+\mathrm{B}\mathrm{a}{\mathrm{I}}_2\to 2\mathrm{K}\mathrm{I}+\mathrm{B}\mathrm{a}\mathrm{B}{\mathrm{r}}_2$.
2. ${\mathrm{K}}^{+}$ pairs with ${\mathrm{I}}^{-}$ and $\mathrm{B}{\mathrm{a}}^{2+}$ pairs with $\mathrm{B}{\mathrm{r}}^{-}$ — partners swapped.
3. A product separates out as a solid (precipitate), typical of such reactions.

Trick: Both sides have two compounds with swapped partners → double displacement.

Answer: (C) Double displacement reaction

Concept: Binary fission is division of a unicellular organism into two daughter cells.

1. In Amoeba, the splitting can occur in any plane (irregular binary fission).
2. In Leishmania, division occurs in a definite plane (longitudinal) because of its flagellum.
3. Plasmodium shows multiple fission; Hydra reproduces by budding (and is not a protozoan).

Yaad rakhein: Amoeba – any plane; Leishmania – definite plane; Plasmodium – multiple fission.

Answer: (B) Amoeba

Concept: Each step of a food chain is a trophic level.

1. 1st level: autotrophs/producers (green plants) fix solar energy.
2. 2nd level: herbivores = primary consumers.
3. 3rd level: small carnivores = secondary consumers; 4th: larger carnivores = tertiary consumers.
4. So options A, B, D misplace the organisms; C is correct.

Yaad rakhein: Producer → Primary (herbivore) → Secondary → Tertiary consumer; only about 10% energy passes to the next level.

Answer: (C) The autotrophs or the producers are at the first trophic level.

Concept: A chemical formula shows the elements in a substance and, through subscripts, how many atoms of each are present.

1. ${\mathrm{H}}_2\mathrm{O}$: subscript 2 → 2 hydrogen atoms, 1 oxygen atom.
2. $\mathrm{C}{\mathrm{O}}_2$: 1 carbon, 2 oxygen atoms.
3. Charge is written as a superscript (e.g. $\mathrm{C}{\mathrm{a}}^{2+}$), not a subscript.

Trick: Subscript (below) = atom count; superscript (above) = charge.

Answer: (D) The number of atoms of each element in a molecule

Concept: When a plant cell is placed in a hypertonic solution, water leaves the cell by osmosis.

1. The cell contents (protoplasm) shrink away from the cell wall.
2. This shrinking is called plasmolysis.
3. The reverse (cell swelling in hypotonic solution) gives turgidity / deplasmolysis.

Yaad rakhein: Plasmolysis = 'plasma moves away' from the wall; seen only in cells with a cell wall.

Answer: (C) Plasmolysis

Concept: Biotic components are living (plants, animals, microbes); abiotic components are non-living (soil, water, air, minerals, temperature).

1. A: Living organisms are biotic, not abiotic → wrong.
2. B: Soil is abiotic, not biotic → wrong.
3. C: Minerals are abiotic → correct.

Trick: 'Bio' = life: if it is alive it is biotic, otherwise abiotic.

Answer: (C) Only C

Concept: Liquids have particles closer than gases but free to slide past each other.

1. Fixed volume: particles are held by fairly strong attraction.
2. No fixed shape: liquid takes the shape of its container.
3. Liquids are almost incompressible and not hard; fixed shape and volume belong to solids; high compressibility to gases.

Yaad rakhein: Solid: fixed shape + volume; Liquid: fixed volume only; Gas: neither.

Answer: (C) It has fixed volume but not fixed shape.

Concept: Acceleration is the rate of change of velocity: $a=\frac{v-u}{t}$.

1. Velocity not changing with time → uniform motion (A is wrong).
2. Change in velocity per unit time → acceleration (B is correct).
3. Free fall → uniform acceleration $g$ (C wrong); velocity varying with time → non-uniform motion (D wrong).

Yaad rakhein: Free fall is the classic example of uniform acceleration ($g\approx 9.8{\text{m/s}}^2$).

Answer: (B) Change in velocity per unit time - Acceleration

Concept: A suspension is a heterogeneous mixture whose solid particles are visible to the naked eye and settle down on standing.

1. Chalk powder in water: particles visible and settle → suspension.
2. Sugar in water → true solution.
3. Few drops of milk in water → colloid; oil in water → emulsion (colloid type).

Yaad rakhein: Suspension examples: chalk/sand/muddy water, flour in water; particle size more than 100 nm.

Answer: (C) Chalk powder in water

Concept: In electrolytic refining, metal ions move from the impure anode through the electrolyte and deposit as pure metal on the cathode.

1. Anode: thick block of impure metal.
2. Cathode: thin strip of pure metal.
3. Electrolyte: solution of a salt of the same metal (e.g. acidified $\mathrm{C}\mathrm{u}\mathrm{S}{\mathrm{O}}_4$ for copper).

Yaad rakhein: Pure metal collects on the pure-metal cathode; impurities fall as anode mud.

Answer: (D) pure metal

Concept: Olfactory indicators change their smell in acidic or basic medium.

1. Vanilla essence, onion and clove oil are olfactory indicators.
2. Vanilla smell disappears in a base but remains in an acid.
3. Phenolphthalein, litmus and methyl orange are visual (colour-change) indicators.

Yaad rakhein: Olfactory = smell: vanilla, onion, clove.

Answer: (B) Vanilla essence

Concept: A triangular prism has two triangular bases and three rectangular lateral faces.

1. Light enters through one lateral face and leaves through another.
2. The angle between these two refracting lateral faces is the angle of prism ($A$).
3. Angle of deviation is the angle between incident ray and emergent ray.

Yaad rakhein: For a prism: $A+\delta =i+e$.

Answer: (D) Angle of prism

Concept: Colloidal particles are too small to be stopped by filter paper and do not settle on their own.

1. Centrifugation spins the mixture very fast.
2. The denser particles are forced to the bottom and separate out.
3. Example: separating cream from milk; blood cells from plasma.

Trick: Filter paper fails for colloids → spin them out (centrifuge).

Answer: (D) Centrifugation

Concept: Newton's first law: a body tends to remain in its state of rest or motion (inertia).

1. When the bus starts suddenly, our feet in contact with the floor move forward with the bus.
2. The upper body, due to inertia of rest, tends to stay where it was.
3. So we fall backwards. (On sudden braking we fall forward — inertia of motion.)

Trick: Bus starts → fall backward; bus stops → fall forward.

Answer: (A) backwards

Concept: Speed = distance ÷ time. In one round of a circle the distance covered is its circumference $2\pi r$.

1. Distance in one round $=2\pi r$.
2. Time for one round $=t$.
3. $v=\frac{2\pi r}{t}$.

Yaad rakhein: $\pi r^2$ is area, not distance — reject such options at once.

Answer: (A) $v=2\pi r/t$

Concept: Evaporation needs latent heat; the liquid takes this heat from its surroundings, which cool down.

1. Sweat on the skin evaporates.
2. The heat needed for evaporation is absorbed from the body surface.
3. So the body loses heat and feels cool.

Yaad rakhein: Same reason: earthen pot cools water; we wear cotton clothes in summer.

Answer: (D) Sweating causes rapid evaporation, which absorbs heat from the body surface and cools the body.

Concept: Displacement is the shortest straight-line distance from initial to final position (with direction); distance is the total path length.

1. A → B: 15 m right; B → A: 15 m left.
2. Final position = initial position A.
3. Displacement $=0\text{m}$ (distance $=15+15=30\text{m}$).

Trick: Back to the starting point → displacement is always zero.

Answer: (A) 0 m