Q&A: practice questions with answers

Concept: Genetic information normally flows DNA → RNA → Protein.

1. Transcription: DNA makes mRNA (in the nucleus).
2. Translation: mRNA is read by ribosomes to make protein.
3. The idea was proposed by Francis Crick (1958).

Trick: Alphabet order: D → R → P (DNA, RNA, Protein). Exception: retroviruses like HIV do RNA → DNA (reverse transcription).

Answer: (C) DNA → RNA → Protein

Concept: Articles 268–270 decide which level levies, collects and keeps a tax.

1. Article 268: duties levied by the Union but collected and kept by the States — for example stamp duty on cheques, promissory notes and bills of exchange.
2. Article 269: levied and collected by the Union, assigned to States; Article 270: taxes shared between Union and States.

Trick: 268 → 'Union levies, State keeps' (stamp duty); 269 → 'Union collects, State gets'; 270 → 'shared'.

Answer: (C) Stamp duties levied by the Union but collected and retained by the States

Concept: Speed = frequency × wavelength, so λ = v/f.

1. v = 340 m/s, f = 680 Hz.
2. λ = 340/680 = 1/2 = 0.5 m.

Trick: 680 is exactly double 340, so λ must be half a metre.

Answer: (A) 0.5 m

Concept: Trade Infrastructure for Export Scheme, launched in 2017 by the Ministry of Commerce & Industry.

1. It gives grants to Central and State agencies for export-linked infrastructure — border haats, land customs stations, testing labs, cold chains, trade centres.
2. Aim: fill infrastructure gaps that make Indian exports costly.

Trick: The name itself says it — 'Trade Infrastructure for Export'.

Answer: (A) Development of export-related infrastructure

Concept: Check A and R separately, then the link.

1. A: The happiness ranking uses GDP per capita, social support, healthy life expectancy, freedom to make life choices, generosity and perceived corruption ⇒ true.
2. R: The report comes from the UN SDSN together with Gallup and Oxford's Wellbeing Research Centre; UNDP is not its publisher ⇒ false.

Trick: UNDP = Human Development Index. Happiness report = SDSN. Finland has topped it for years.

Answer: (C) A is true, but R is false.

Concept: A carbon sink takes in more CO₂ than it gives out.

1. Forests, plants and soil absorb CO₂ and lock it away, reducing greenhouse gases.
2. India's NDC target: an additional sink of 2.5–3 billion tonnes CO₂-equivalent by 2030 through more forest and tree cover.
3. Deforestation, fossil fuels and single-species plantations weaken sinks.

Trick: Three options harm the environment — only (B) helps it.

Answer: (B) To capture and store carbon dioxide in forests, vegetation, and soil

Concept: Inward-looking trade policy of early Five Year Plans.

1. A: India replaced imports with home-made goods using tariffs and quotas ⇒ true.
2. R: Purpose was to shield infant domestic industries from foreign competition ⇒ true.
3. R gives the very reason for A ⇒ R explains A.

Trick: Ask 'A because R?' — 'India substituted imports because it wanted to protect new industries' reads naturally, so (A).

Answer: (A) Both A and R are true, and R correctly explains A.

Concept: Nothing, not even light, can come out from within a black hole's event horizon.

1. The X-rays seen near black holes come from very hot gas in the accretion disk outside the horizon ⇒ Statement 1 wrong.
2. Pulsars are highly magnetised neutron stars spinning very fast and sending beams of radiation ⇒ Statement 2 correct.

Yaad rakhein: Pulsars were discovered in 1967 by Jocelyn Bell Burnell.

Answer: (B) 2 only

Concept: During a National Emergency, Parliament can make laws on State List subjects.

1. This power comes from Article 250.
2. Such laws lapse 6 months after the Emergency ends.
3. Art. 352 only proclaims the Emergency; Art. 254 deals with Union–State law conflict; Art. 256 with State obligation to obey Union laws.

Trick: Parliament on State List: Art. 249 (Rajya Sabha resolution), 250 (Emergency), 252 (two or more States request), 253 (treaties).

Answer: (A) Article 250

Concept: Article 131A came with the 42nd Amendment (1976) and went with the 43rd (1977).

1. Its power to judge the validity of Central laws was given only to the Supreme Court, never to High Courts ⇒ Statement 1 is incorrect.
2. The Janata government repealed it through the 43rd Amendment in 1977 ⇒ Statement 2 is correct.

Trick: The '131' series (131, 131A) is about the Supreme Court's original jurisdiction — so 'High Courts' is wrong at sight.

Answer: (B) 2 only

Concept: Write the decimal part over a power of 10 and simplify.

1. $4.625=\frac{4625}{1000}$.
2. Divide by 125: $4625÷125=37$, $1000÷125=8$.
3. $4.625=\frac{37}{8}$.

Trick: $0.625=\frac{5}{8}$ (memorise eighths: 0.125, 0.25, 0.375, 0.5, 0.625…). So $4\frac{5}{8}=\frac{32+5}{8}=\frac{37}{8}$.

Answer: (A) $\frac{37}{8}$

Concept: If x% of a = y% of b, then a : b = y : x.

1. $\frac{20}{100}a=\frac{15}{100}b\Rightarrow 20a=15b$.
2. $\frac{a}{b}=\frac{15}{20}=\frac{3}{4}$.
3. a : b = 3 : 4.

Trick: Cross the percentages: a : b = 15 : 20 = 3 : 4.

Answer: (B) 3 : 4

Concept: a : b :: c : d means $a\times d=b\times c$.

1. $(5-x)(12-x)=(8-x)(7-x)$.
2. $60-17x+x^2=56-15x+x^2$.
3. $4=2x\Rightarrow x=2$. Check: 3 : 6 = 5 : 10 = 1 : 2 ✓.

Trick: Shortcut $x=\frac{ad-bc}{a+d-b-c}=\frac{60-56}{17-15}=2$.

Answer: (A) 2

Concept: Convert everything to decimals, solve the bracket first.

1. $\frac{27}{8}$ is $2\frac{7}{8}=2.875$ (the mixed number in the question).
2. Bracket sum: $2.875+2.750=5.625$.
3. Difference: $7.400-5.625=1.775$.

Trick: Last decimal digit: $0.400-0.625$ ends in 5 — only 1.775 and 2.025 fit; the bracket ≈ 5.6, so $7.4-5.6\approx 1.8\Rightarrow 1.775$.

Answer: (B) 1.775

Concept: Profit share $\propto$ capital $\times$ time (in months).

1. Sumit: ₹80k for months 1–6 and ₹120k for months 7–12 ⇒ $(80+120)\times 6=1200$ (₹ thousand-months).
2. Sachin: in from month 4 to month 9 = 6 months ⇒ $100\times 6=600$.
3. Ratio = 1200 : 600 = 2 : 1.

Trick: Both of Sumit's periods are 6 months, so just add his capitals ($80+120=200$) and compare with Sachin's 100 for the same 6 months ⇒ 2 : 1.

Answer: (B) 2 : 1

Concept: New person = new total − old total.

1. Old total = $21\times 17=357$.
2. New total = $22\times 20=440$.
3. Teacher = $440-357=83$ years.

Trick: Teacher = new average + (old count $\times$ rise) = $20+21\times 3=83$.

Answer: (B) 83

Concept: Use deviations from the overall average.

1. 40 people are ₹10,000 above ₹58,000 ⇒ excess = $40\times 10,000=$ ₹4,00,000.
2. The other 50 must be short by the same ₹4,00,000 ⇒ ₹8,000 each.
3. Average = $58,000-8,000=$ ₹50,000.

Trick: Deviation method avoids big totals: $(40\times 10,000)÷50=8,000$ below.

Answer: (C) ₹50,000

Concept: Under CI, if money becomes k times in T years, it becomes $k^n$ times in nT years.

1. 2 times in 3 years.
2. $64=2^6\Rightarrow n=6$.
3. Time = $6\times 3=18$ years.

Trick: Keep doubling: 2(3), 4(6), 8(9), 16(12), 32(15), 64(18 years).

Answer: (D) 18

Concept: $\text{SP}=\text{CP}-\text{Loss}$.

1. Loss : CP = 1 : 5 ⇒ take Loss = 1, CP = 5.
2. $\text{SP}=5-1=4$.
3. SP : CP = 4 : 5.

Trick: Loss is $\frac{1}{5}=20\%$ ⇒ SP is 80% of CP $=\frac{4}{5}$.

Answer: (B) 4 : 5

Concept: $\text{SP}=\text{MP}\times (1-d\%)$, and $\text{CP}=\text{SP}÷(1+p\%)$.

1. $\text{SP}=300\times \frac{80}{100}=$ ₹240.
2. $\text{CP}=240\times \frac{100}{125}=240\times \frac{4}{5}$.
3. $\text{CP}=$ ₹192.

Trick: $25\%$ profit $=\frac{1}{4}$ ⇒ CP : SP = 4 : 5. So $\text{CP}=\frac{4}{5}\times 240=192$.

Answer: (A) ₹192