Given below are two statements, one is labelled asAssertion (A) :and the other as Reason (R).Assertion (A):The highest concentration of Seismic zones lies in Himalayan region in India.Reason (R):There are many longitudinal thrust zones in Himalayas.

1. A

   Both (A) and (R) are true and (R) is the correct explanation of (A)

   (a) Both (A) and (R) true and (R) explains (A). The Himalaya is India’s densest seismic belt (Zones IV–V). Longitudinal thrusts—MBT, MCT, MFT—are the plate-boundary faults along which strain is released. That mechanism is why the assertion holds, so (R) is the correct explanation.

2. B

   Both (A) and (R) are true, but (R) is not the correct explanation of (A)

   (b) Both true but (R) does not explain (A). The thrusts are not a side fact; they are the reason the Himalayan arc is so seismic.

3. C

   (A) is true, but (R) is false

   (c) (A) true, (R) false. Longitudinal thrust zones (Main Central Thrust, Main Boundary Thrust, Himalayan Frontal Thrust) are standard Himalayan structure, so (R) is not false.

4. D

   (A) is false, but (R) is true

   (d) (A) false, (R) true. (A) is not false: BIS seismic zonation puts the highest hazard along the Himalaya, not the peninsula.

Summary. Official key is (a). Both are true and (R) explains (A). India’s strongest earthquake concentration follows the Himalayan collision. Many longitudinal thrusts (MCT, MBT, MFT) store and release that strain. Honour the stored letter (a).