Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R). Assertion (A): Maximum number of the species of butterflies are found in tropical countries. Reason (R): Butterflies can not tolerate low temperatures. Select the correct answer using the codes given below:

Option A is correct. Both the assertion and the reason are true, and the reason actually explains the assertion.

Assertion: Butterfly diversity peaks in the tropics. Warm, humid, stable climates with year-round food plants (especially flowering and host plants) support far more species than temperate or polar regions. This is the latitudinal diversity gradient seen in most insect groups.

Reason: Butterflies are ectotherms. Their flight muscles and metabolism depend on ambient heat, so they cannot remain active or complete their life cycle in prolonged cold. This physiological limit shrinks their range toward the tropics, which is why the tropics hold the most species.

• B is wrong because it denies the link between the two statements. The cold-tolerance limit is the direct explanation for the tropical concentration.
• C is wrong because the reason is accepted as true in standard ecology texts.
• D is wrong because the assertion is a well-documented biogeographic fact.

Mains angle: this links to biogeography, climate change shifting butterfly ranges poleward, and the conservation value of tropical habitats.

Trap: Aspirants sometimes pick B by treating the reason as a general fact that does not explain the assertion. Ask whether the reason would account for the pattern if it were true; here it does.