Assertion (A) : Narmada and Tapti rivers do not form deltas. Reason (R) : These rivers form estuaries.

The correct answer is Option 2. Both the Assertion (A) and the Reason (R) are factually correct statements, but (R) does not serve as the causal explanation for (A).

Assertion (A) is true: The Narmada and Tapti are west-flowing rivers that do not form deltas. This is primarily because they flow through hard rock "rift valleys" with steep gradients, resulting in high velocity and minimal silt collection. Without sufficient sediment load, delta formation is impossible.

Reason (R) is true: These rivers form estuaries, which are tidal mouths where freshwater meets saltwater. However, forming an estuary is a result of the same geological conditions (lack of silt and high speed) rather than the reason why a delta is absent. The absence of a delta is due to the lack of sediment and the nature of the terrain, not merely because an estuary exists.