Q&A: practice questions with answers

Concept: Saturated carbon compounds contain only single C–C bonds.

1. Alkanes (${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$) have only single bonds — saturated.
2. Alkenes (e.g. ethylene ${\mathrm{C}}_2{\mathrm{H}}_4$) have a double bond — unsaturated.
3. Alkynes have a triple bond — unsaturated.

Trick: Alk-ane = all single bonds; -ene = double; -yne = triple.

Answer: (D) Alkane

Concept: Match each named reaction with its true example.

1. (a) Ethanol + conc. ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ → ethene is dehydration, not saponification — wrong.
2. (b) Ethanoic acid + ethanol (acid catalyst) → ester is esterification — correct.
3. (c) Ester + NaOH → sodium salt of acid is saponification, not dehydration — wrong.

Trick: (a) and (c) have their names swapped; only (b) is right.

Answer: (C) Only (b) is correct.

Concept: A metal is more reactive than all metals below it in the reactivity series.

1. Series (part): $\mathrm{K}>\mathrm{N}\mathrm{a}>\mathrm{C}\mathrm{a}>\mathrm{M}\mathrm{g}>\mathrm{A}\mathrm{l}>\mathrm{Z}\mathrm{n}>\mathrm{F}\mathrm{e}>\mathrm{P}\mathrm{b}>\mathrm{H}>\mathrm{C}\mathrm{u}>\mathrm{H}\mathrm{g}>\mathrm{A}\mathrm{g}>\mathrm{A}\mathrm{u}$.
2. K, Na and Ca are above copper — more reactive than Cu.
3. Silver is below copper, so Cu displaces Ag from $\mathrm{A}\mathrm{g}\mathrm{N}{\mathrm{O}}_3$ solution.

Trick: $\mathrm{C}\mathrm{u}+2\mathrm{A}\mathrm{g}\mathrm{N}{\mathrm{O}}_3\to \mathrm{C}\mathrm{u}(\mathrm{N}{\mathrm{O}}_3{)}_2+2\mathrm{A}\mathrm{g}$ proves $\mathrm{C}\mathrm{u}>\mathrm{A}\mathrm{g}$.

Answer: (B) Silver

Concept: Biodegradable materials are broken down by biological processes.

1. Decomposers — mainly bacteria and fungi — act on such wastes.
2. They break complex organic matter into simple substances that return to the soil.
3. Sunlight and wind are physical agents; viruses do not decompose waste.

Yaad rakhein: Biodegradable = broken down by microbes (bacteria, fungi); plastics are non-biodegradable.

Answer: (C) Bacteria

Concept: Use $v=u+at$ and $s=ut+\frac{1}{2}a{t}^2$ with retardation $a=-2{\text{m s}}^{-2}$.

1. Final $v=0$, $t=10\text{s}$: $0=u-2\times 10\Rightarrow u=20{\text{m s}}^{-1}$.
2. $s=20\times 10-\frac{1}{2}\times 2\times {10}^2=200-100=100\text{m}$.
3. Check: $s=\frac{u^2}{2a}=\frac{400}{4}=100\text{m}$.

Trick: Stopping uniformly: $s=\frac{1}{2}a{t}^2=\frac{1}{2}\times 2\times {10}^2=100\text{m}$ (reverse motion).

Answer: (D) 100 m

Concept: Sperms travel from the testes to the urethra through the vas deferens.

1. Cutting and tying the vas deferens (vasectomy) blocks this path.
2. So sperms cannot be transferred, though other functions remain.
3. Fallopian tube is a female organ; cutting it (tubectomy) blocks the egg.

Yaad rakhein: Vasectomy → vas deferens (male); Tubectomy → fallopian tube (female).

Answer: (C) vas deferens

Concept: Fine air particles scatter shorter wavelengths much more strongly than longer ones.

1. Among visible colours, blue has a short wavelength; red has the longest.
2. So blue light is scattered the most in the atmosphere.
3. This is why the clear sky appears blue.

Yaad rakhein: Most scattered = blue (sky blue); least scattered = red (danger signals, sunset).

Answer: (A) blue

Concept: Compressibility depends on the space between particles.

1. Solids: particles tightly packed — almost incompressible.
2. Liquids: little space — very slightly compressible.
3. Gases: large intermolecular spaces — highly compressible (e.g. CNG, LPG cylinders).

Trick: CNG/LPG cylinders store large gas volumes only because gases compress easily.

Answer: (C) The gaseous state

Concept: Glucose → pyruvate (cytoplasm); pyruvate's fate depends on oxygen and organism.

1. (i) Yeast, no oxygen: pyruvate → ethanol + $\mathrm{C}{\mathrm{O}}_2$ — correct.
2. (ii) Aerobic breakdown of pyruvate occurs in mitochondria, not chloroplast — wrong.
3. (iii) Muscles, lack of oxygen: pyruvate → lactic acid — correct.

Yaad rakhein: Chloroplast = photosynthesis; mitochondria = aerobic respiration.

Answer: (C) Only (i) and (iii)

Concept: Isobars are atoms of different elements having the same mass number but different atomic numbers.

1. Example: ${\mathrm{}}_{20}^{40}\mathrm{C}\mathrm{a}$ and ${\mathrm{}}_{18}^{40}\mathrm{A}\mathrm{r}$.
2. Different atomic numbers → different protons and electrons.
3. Same mass number (total nucleons) → same atomic mass.

Trick: Isobars = same atomic mass; Isotopes = same atomic number (protons).

Answer: (B) same atomic mass

Concept: From Newton's law, $F=\frac{GMm}{r^2}$, so $G=\frac{F{r}^2}{Mm}$.

1. Units: $\frac{\text{N}\times {\text{m}}^2}{\text{kg}\times \text{kg}}$.
2. $={\text{N m}}^2{\text{kg}}^{-2}$.
3. Value: $G=6.67\times {10}^{-11}{\text{N m}}^2{\text{kg}}^{-2}$.

Trick: Two masses in the denominator → ${\text{kg}}^{-2}$.

Answer: (B) ${\text{N m}}^2{\text{kg}}^{-2}$

Concept: Earth's atmosphere has layers of different density, hence different refractive index.

1. Starlight bends towards the normal as it passes into denser layers.
2. So the star appears slightly higher than its actual position.
3. Because these layers keep shifting, the apparent position keeps changing slightly.

Yaad rakhein: Same cause explains twinkling of stars — changing atmospheric refraction.

Answer: (C) Different layers of the atmosphere have different density

Concept: Brain, spinal cord and nerves are all made of nervous tissue.

1. Nervous tissue consists of neurons that receive and conduct impulses.
2. The spinal cord carries messages between the brain and the body and controls reflexes.
3. Other tissues (connective, epithelial, muscular) only support or protect it.

Yaad rakhein: Nervous system (brain + spinal cord + nerves) = nervous tissue (neurons).

Answer: (A) Nervous tissue

Concept: Check each statement about general properties of metals.

1. 1. Beating into thin sheets = malleability — correct (e.g. gold, aluminium foil).
2. 2. Drawing into wires = ductility — correct (e.g. copper wire).
3. 3. Metals are good conductors of heat — correct (silver and copper are best).

Yaad rakhein: Malleable → sheets; Ductile → wires; lead and mercury are poor heat conductors among metals.

Answer: (C) 1, 2 and 3

Concept: Every two masses attract each other by the gravitational force.

1. The Sun's gravitational pull provides the centripetal force on each planet.
2. This force keeps the planets moving in nearly circular (elliptical) orbits.
3. Similarly, Earth's gravity keeps the Moon in orbit.

Yaad rakhein: Orbits of planets, Moon and satellites → gravitational force.

Answer: (D) Gravitational

Concept: Alpha particles fired at thin gold foil showed how mass and charge are arranged in an atom.

1. Most passed straight → most of the atom is empty space.
2. A few deflected and very few (about 1 in 12000) bounced back → a tiny, dense, positively charged nucleus.
3. Negatively charged electrons revolve around the nucleus.

Yaad rakhein: Uniform positive sphere = Thomson; indivisible solid sphere = Dalton; nucleus + electrons = Rutherford.

Answer: (C) Atoms consist of a positively charged nucleus and negatively charged electrons.

Concept: Field at the centre of a coil: $B=\frac{{\mu }_{0}nI}{2r}$, so $B\propto n$.

1. Each turn adds its own field in the same direction.
2. With $n=10$ turns and same $I$, $r$: $B^{\prime }=10\times B$.
3. So the field becomes $10B$.

Trick: $n$ turns → $n$ times the field of one turn.

Answer: (A) 10B

Concept: Any current-carrying conductor produces a magnetic field around it.

1. I: A current-carrying coil produces a magnetic field (Oersted's discovery) — correct.
2. II: A solenoid's field lines are like a bar magnet's; one end acts as N, the other as S — correct.
3. Both statements are true.

Yaad rakhein: Solenoid + soft iron core = electromagnet.

Answer: (D) Both Statements I and II

Concept: The penis is the male copulatory organ.

1. Sperms made in testes pass through vas deferens and urethra.
2. During mating, the penis delivers sperms into the female reproductive tract (vagina).
3. Eggs and polar bodies are female cells; the zygote forms only after fertilisation.

Yaad rakhein: Testes → make sperms; penis → transfers sperms.

Answer: (A) sperms

Concept: Isomers are compounds with the same molecular formula but different structures.

1. Example: ${\mathrm{C}}_4{\mathrm{H}}_{10}$ exists as n-butane (straight chain) and iso-butane (branched).
2. Same atoms, different arrangement → different properties.
3. Same formula + same structure would be the same compound, not isomers.

Trick: Iso = same (formula); mer = parts arranged differently.

Answer: (C) They have the same molecular formula but different structural arrangements.