Assertion Reason
Key Concepts
| # | Concept | Explanation |
|---|---|---|
| 1 | Assertion (A) | The statement that is presented as a fact in the question. |
| 2 | Reason (R) | The statement that is given as the supposed explanation for the Assertion. |
| 3 | Both true & R explains A | Both statements are factually correct and R is the correct scientific/logical cause of A. |
| 4 | Both true but R does NOT explain A | Both statements are individually correct, but R is unrelated to A. |
| 5 | A true, R false | Assertion is correct but Reason contradicts established facts. |
| 6 | A false, R true | Assertion is factually wrong even though the Reason by itself is correct. |
| 7 | Both false | Both statements are factually incorrect. |
| 8 | Golden check | Always treat R independently first—if R is false, options claiming “R explains A” collapse automatically. |
15 Practice MCQs
1. Assertion (A): Sound travels faster in steel than in air.
Reason (R): Steel has higher density than air.
Ans: (b) Both A and R are true but R is NOT the correct explanation of A.
Solution: A is true. R is also true (steel is denser). However, the speed of sound depends on modulus of elasticity & density together; the higher speed in steel is mainly due to its very high elastic modulus, not merely density. Thus R does not correctly explain A.
Trick: “Density alone never decides speed of sound—check modulus.”
Tag: Physics, Sound
2. Assertion (A): A freely falling body experiences weightlessness.
Reason (R): The acceleration due to gravity is zero at the centre of the earth.
Ans: (d) A is true but R is false.
Solution: Weightlessness arises because the effective reaction force is zero, not because g becomes zero. g at the centre is indeed zero, but that fact is irrelevant to the phenomenon of weightlessness during free fall near the surface.
Trick: “Free-fall ⇒ no reaction; g=0 inside earth ≠ weightlessness outside.”
Tag: Physics, Mechanics
3. Assertion (A): The planet Mars appears red from Earth.
Reason (R): Mars contains iron oxide on its surface.
Ans: (a) Both A and R are true and R correctly explains A.
Solution: Iron oxide (rust) reflects reddish light → Mars looks red.
Trick: “Rust = red; Mars has rust.”
Tag: General Science, Astronomy
4. Assertion (A): In India, the monsoon rainfall decreases from east to west.
Reason (R): The monsoon winds blow from the Bay of Bengal towards the Indian mainland.
Ans: (a) Both A and R are true and R correctly explains A.
Solution: Moisture-laden winds start from the east; lose moisture while moving west → east gets more rain.
Trick: “Enter moist → exit dry.”
Tag: Geography, Indian Monsoon
5. Assertion (A): CO₂ is used in fire extinguishers.
Reason (R): CO₂ is heavier than air and does not support combustion.
Ans: (a) Both A and R are true and R correctly explains A.
Solution: CO₂ blankets the fire, cutting off oxygen.
Trick: “Blanket gas = heavier + non-supporter.”
Tag: Chemistry
6. Assertion (A): A horse can pull a cart even in vacuum.
Reason (R): Action-reaction forces are equal and opposite.
Ans: (d) A is false but R is true.
Solution: Pulling needs friction between hooves & ground; in vacuum there is no air but ground contact is still needed. Horse cannot accelerate a cart on perfectly smooth, friction-less ground. R (Newton’s 3rd law) is always true but does not validate A here.
Trick: “Motion needs external reaction; vacuum ≠ friction.”
Tag: Physics, Newton Laws
7. Assertion (A): A lunar eclipse never occurs on every new moon.
Reason (R): The moon’s orbital plane is inclined ~5° to the ecliptic.
Ans: (a) Both A and R are true and R correctly explains A.
Solution: Inclination prevents perfect alignment every month.
Trick: “Tilted orbit → rare eclipse.”
Tag: Astronomy
8. Assertion (A): Ice floats on water.
Reason (R): Ice has lower density than water.
Ans: (a) Both A and R are true and R correctly explains A.
Trick: “Density down → floats.”
Tag: Physics, Matter
9. Assertion (A): The Indian Railways is divided into zones for operational convenience.
Reason (R): India is the second largest country by population.
Ans: (b) Both A and R are true but R does NOT explain A.
Solution: Zoning is for logistics, not directly because of population rank.
Trick: “Zoning ≠ population rank; zoning = manageability.”
Tag: Indian Railways GK
10. Assertion (A): LED bulbs are preferred over CFLs.
Reason (R): LEDs do not emit UV radiation.
Ans: (b) Both A and R are true but R is NOT the main/complete explanation. (Railways often treat this as “R does not correctly explain A”).
Solution: Main reasons: energy efficiency, longer life, instant glow. No UV is an auxiliary benefit.
Trick: “Key driver = efficiency + life.”
Tag: General Science, Technology
11. Assertion (A): A train’s platform ticket is cheaper than its cheapest journey ticket.
Reason (R): Platform tickets are subsidised by passenger fares.
Ans: (a) Both A and R are true and R correctly explains A.
Solution: Indian Railways cross-subsidises platform tickets so that only travellers pay for travel, visitors pay nominal charge.
Trick: “Cross-subsidy keeps platform cheap.”
Tag: Railways Policies
12. Assertion (A): A cyclone in the Arabian Sea can move towards Western India.
Reason (R): All cyclones originate only in the Bay of Bengal.
Ans: (c) A is true but R is false.
Solution: Cyclones form in both seas; R is factually wrong.
Trick: “Two basins: Bay + Arabian.”
Tag: Geography
13. Assertion (A): The GST replaced many indirect taxes in India.
Reason (R): GST is a value-added tax levied uniformly across states.
Ans: (a) Both A and R are true and R correctly explains A.
Trick: “One nation, one tax → subsumes many.”
Tag: Economics, Polity
14. Assertion (A): A rainbow can be seen when the sun is behind the observer.
Reason (R): Dispersion of sunlight occurs due to raindrops acting like tiny prisms.
Ans: (a) Both A and R are true and R correctly explains A.
Trick: “Sun back + drop prism → bow.”
Tag: Physics, Optics
15. Assertion (A): A goods train is often longer than a passenger train.
Reason (R): Goods trains carry heavier axle loads.
Ans: (b) Both A and R are true but R does NOT explain A.
Solution: Length is for volume; axle load is for weight per wheel. They are different design choices.
Trick: “Length ≠ load; length = capacity.”
Tag: Railways GK
Speed Tricks
| Situation | Shortcut | Example |
|---|---|---|
| 1. R is clearly false | Mark options having “R true” as WRONG; choose among remaining in 2 s | Q12 above: R says “only Bay of Bengal” → false, strike (a) & (b) |
| 2. Absolute words in R (“only”, “always”, “never”) | 70 % chance R is false | “Sun always rises in east” is true, but “cyclones always originate in Bay” is false |
| 3. Cause-effect keywords (“because”, “due to”) | Check whether removing R still leaves A intact; if yes, R is not the cause | Q9: A is true even if you forget India’s population rank → R does not explain A |
| 4. Numerical data given | Verify R first; if number wrong, R false → eliminate two options quickly | “Speed of sound in air 3300 m/s” → R false |
| 5. Both statements look true but from different domains | Suspect (b) – “true but no explanation” | Q15: length (operations) vs axle load (engineering) → different domains |
Quick Revision
| Point | Detail |
|---|---|
| 1 | Treat R independently; if R false, kill (a) & (b) instantly. |
| 2 | “Both true & R explains A” needs (i) fact correctness (ii) logical causality. |
| 3 | Absolute words (“only/always”) in R often make it false. |
| 4 | A can be false even when R is a textbook fact. |
| 5 | In geography questions, direction (east→west, north→south) is a favourite causal link. |
| 6 | Physics: density-related reasons—cross-check with Archimedes or speed formula. |
| 7 | Biology: enzyme/RBC questions—check pH, temperature optima; small factual error makes R false. |
| 8 | Economics: GST, subsidies—R must match the policy objective cited in A. |
| 9 | Railways-specific: zone/heel/layout questions—verify with latest RRBI site if possible; otherwise pick the most general truth. |
| 10 | When in 50-50 doubt, apply “minimum assumption” rule: choose the option that needs no extra data. |
BETA
