Q&A: practice questions with answers

Concept: Work is done when a force produces displacement in its direction.

1. $W=F\times s$ (force and displacement along the same direction).
2. In general, $W=Fs\cos \theta$.
3. SI unit: joule ($1\text{ J}=1\text{ N}\times 1\text{ m}$).

Trick: Work is a product, never a sum or difference: $W=F\times s$.

Answer: (A) force × displacement

Concept: The thyroid gland makes the hormone thyroxine, which needs iodine.

1. Thyroxine regulates carbohydrate, protein and fat metabolism.
2. Iodine deficiency → less thyroxine → swollen neck (goitre).
3. That is why iodised salt is recommended.

Yaad rakhein: Iodine → Thyroid → Thyroxine; deficiency → Goitre.

Answer: (A) Thyroid gland

Concept: In free fall, the body moves only under gravity with constant acceleration $g\approx 9.8\mathrm{m}{\mathrm{s}}^{-2}$.

1. Mass of the body does not change.
2. $G=6.67\times {10}^{-11}\mathrm{N}{\mathrm{m}}^2\mathrm{k}{\mathrm{g}}^{-2}$ is a universal constant.
3. Acceleration $g$ stays constant near the Earth.
4. Distance fallen keeps increasing: $s=\frac{1}{2}g{t}^2$ – it does NOT remain constant.

Trick: In free fall, velocity and distance change; $g$, $G$ and mass stay fixed.

Answer: (C) Distance

Concept: A decomposition reaction caused by heat is called thermal decomposition.

1. Limestone (calcium carbonate) on heating gives quicklime and carbon dioxide.
2. $\mathrm{C}\mathrm{a}\mathrm{C}{\mathrm{O}}_3\stackrel{\mathrm{\Delta }}{\to }\mathrm{C}\mathrm{a}\mathrm{O}+\mathrm{C}{\mathrm{O}}_2$
3. Only a carbonate can release $\mathrm{C}{\mathrm{O}}_2$, so the answer is calcium carbonate.

Trick: Need $\mathrm{C}{\mathrm{O}}_2$ as product → look for carbonate ($\mathrm{C}{\mathrm{O}}_3$).

Answer: (B) Calcium carbonate

Concept: Mechanical energy = kinetic energy + potential energy.

1. Kinetic energy: $E_k=\frac{1}{2}m{v}^2$ (due to motion).
2. Potential energy: $E_p=mgh$ (due to position or shape).
3. Light, heat and chemical energy are other forms, not parts of mechanical energy.

Yaad rakhein: Mechanical energy = KE + PE only.

Answer: (D) Potential energy

Concept: A solenoid is a long coil of many turns of insulated wire.

1. Inside the solenoid the field lines are parallel straight lines → field is uniform. (i) true.
2. Outside, the lines spread out, so the field is much weaker – not equal to inside. (ii) false.
3. The field pattern resembles that of a bar magnet, with N and S ends. (iii) true.

Yaad rakhein: Solenoid = bar magnet; uniform field inside (used to make electromagnets).

Answer: (A) Both (i) and (iii)

Concept: Fragmentation: the body breaks into pieces and each piece grows into a new individual.

1. Example: Spirogyra (a filamentous alga).
2. It is possible only when the body is simply organised, since every fragment can regrow the whole body.
3. Complex organisms have specialised organs and cannot regrow from fragments; unicellular organisms use fission instead.

Yaad rakhein: Fragmentation → simple multicellular (Spirogyra); fission → unicellular.

Answer: (A) only in simple body organised multicellular organisms

Concept: Photosynthesis: $6\mathrm{C}{\mathrm{O}}_2+12{\mathrm{H}}_2\mathrm{O}\to {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{O}}_2+6{\mathrm{H}}_2\mathrm{O}$ (in presence of sunlight and chlorophyll).

1. The glucose made is first used by the plant to provide energy (respiration).
2. The remaining carbohydrate is stored as starch – the internal energy reserve of plants.
3. Glycogen is the storage form in animals, not plants.

Yaad rakhein: Plants store starch; animals store glycogen.

Answer: (C) First, carbohydrates are utilised for energy production and the rest are stored in the form of starch.

Concept: Plaster of Paris (POP) is calcium sulphate hemihydrate, $\mathrm{C}\mathrm{a}\mathrm{S}{\mathrm{O}}_4·\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$.

1. On mixing with water it sets into a hard mass of gypsum: $\mathrm{C}\mathrm{a}\mathrm{S}{\mathrm{O}}_4·\frac{1}{2}{\mathrm{H}}_2\mathrm{O}+1\frac{1}{2}{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}\mathrm{a}\mathrm{S}{\mathrm{O}}_4·2{\mathrm{H}}_2\mathrm{O}$.
2. This property is used for plaster casts supporting fractured bones, toys, decorative items and smooth surfaces.
3. Washing soda removes hardness; baking soda is used in baking and fire extinguishers.

Trick: POP + water → hard gypsum → bone cast.

Answer: (D) Creating casts for supporting fractured bones

Concept: A bisexual flower has both stamens (male) and pistil (female); a unisexual flower has only one of them.

1. Mustard and Hibiscus flowers have both stamens and pistil → bisexual.
2. Papaya and watermelon have separate male and female flowers → unisexual.
3. Pumpkin (cucurbit) flowers are also unisexual.

Yaad rakhein: Bisexual: Mustard, Hibiscus; Unisexual: Papaya, Watermelon (and cucurbits).

Answer: (B) Mustard

Concept: Meristems are growing tissues whose cells keep dividing.

1. Apical meristem – at the tips of stem and root – increases the length.
2. Lateral meristem (cambium) increases the girth (thickness).
3. Intercalary meristem – at the base of leaves or internodes – also adds to length.

Yaad rakhein: Apical = Apex = Length; Lateral = Girth.

Answer: (B) length

Concept: The number of heart chambers differs among vertebrate groups.

1. Fishes: 2 chambers (1 atrium + 1 ventricle).
2. Amphibians (and most reptiles): 3 chambers (2 atria + 1 ventricle), so oxygenated and deoxygenated blood mix slightly.
3. Birds and mammals: 4 chambers – complete separation of blood.

Yaad rakhein: Fish 2, Amphibian 3, Bird/Mammal 4.

Answer: (A) Amphibians

Concept: Vegetative propagation: new plants grow from vegetative parts – root, stem or leaf.

1. Leaves: Bryophyllum (buds on leaf margins).
2. Stem: potato, sugarcane, rose cuttings; Root: sweet potato, dahlia.
3. The flower is a reproductive part used for sexual reproduction, so it does not take part.

Yaad rakhein: Vegetative = root, stem, leaf; flower = sexual reproduction.

Answer: (D) Flower

Concept: The magnetic field at the centre of a current-carrying coil is $B\propto \frac{nI}{r}$.

1. Field increases when current $I$ is increased.
2. Field increases when number of turns $n$ is increased.
3. Field decreases as we move away from the coil.
4. So only 'current is increased' raises the field.

Trick: More current, more turns → stronger field; more distance → weaker.

Answer: (D) current through the coil is increased

Concept: Newton's law: $F=\frac{G{m}_1{m}_2}{d^2}$, so $F\propto m_1{m}_2$.

1. New mass $m_1^{\prime }=4m_1$, $m_2$ and $d$ unchanged.
2. $F^{\prime }=\frac{G(4m_1)m_2}{d^2}=4\times \frac{G{m}_1{m}_2}{d^2}$
3. $F^{\prime }=4F$

Trick: Force changes in the same ratio as the product of masses.

Answer: (D) 4F

Concept: Alkenes have general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$; successive members differ by $\mathrm{C}{\mathrm{H}}_2$.

1. ${\mathrm{C}}_3{\mathrm{H}}_6$: $n=3$, $2n=6$ ✓; ${\mathrm{C}}_4{\mathrm{H}}_8$: $n=4$, $2n=8$ ✓ – both alkenes, differ by $\mathrm{C}{\mathrm{H}}_2$.
2. $\mathrm{C}{\mathrm{H}}_4$ and ${\mathrm{C}}_2{\mathrm{H}}_6$ are alkanes (${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$).
3. ${\mathrm{C}}_3{\mathrm{H}}_{10}$ is not a valid hydrocarbon; so only (A) fits.

Yaad rakhein: Alkane ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$, Alkene ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$, Alkyne ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}$.

Answer: (A) ${\text{C}}_3{\text{H}}_6$ and ${\text{C}}_4{\text{H}}_8$

Concept: The alimentary canal runs from mouth to anus: oesophagus → stomach → small intestine → large intestine.

1. The small intestine is the longest part (about 6–7 m in adults), highly coiled.
2. Its length gives a large surface for complete digestion and absorption (villi).
3. The large intestine is shorter (about 1.5 m) but wider.

Yaad rakhein: Small intestine = longest; large intestine = wider, not longer.

Answer: (D) Small intestine

Concept: Standard rays for a concave mirror: a ray parallel to the principal axis passes through F after reflection, and vice versa.

1. The path of light is reversible.
2. So a ray passing through the principal focus F, after reflection, emerges parallel to the principal axis.
3. A ray through C retraces its path; a ray to the pole reflects at an equal angle.

Yaad rakhein: Parallel → F, and F → Parallel.

Answer: (C) emerge parallel to the principal axis

Concept: A solution is a homogeneous mixture of two or more substances.

1. Particle size is less than 1 nm (${10}^{-9}$ m) – true.
2. Particles are too small to scatter light, so no Tyndall effect – true.
3. Solute particles pass through filter paper and cannot be separated by filtration – so (D) is NOT a characteristic.

Yaad rakhein: Solution: no Tyndall effect, no settling, not separable by filtration.

Answer: (D) The solute particles can be separated from the mixture by the process of filtration.

Concept: The pH scale runs from 0 to 14 and measures ${\mathrm{H}}^{+}$ ion concentration.

1. pH less than 7 → acidic.
2. pH = 7 → neutral (e.g. pure water).
3. pH greater than 7 → basic (alkaline).

Yaad rakhein: Pure water at room temperature has pH exactly 7.

Answer: (D) 7