Step 1: Analyzing the statement. The statement mentions that alluvial soil is useful for paddy, wheat, and pulses, which is correct. Alluvial soil, which is formed by the deposition of silt and clay through water, is indeed fertile and ideal for the cultivation of paddy, wheat, and pulses.
Step 2: Analyzing the reason. The reason provided states that alluvial soil is famous for moisture. This is partially true, as alluvial soil is known for its moisture retention capacity. However, the reason does not directly explain why alluvial soil is suitable for the mentioned crops. The suitability of alluvial soil for crops is primarily due to its fertility, not just its moisture content.
Step 3: Conclusion.
While both the statement and the reason are correct, the reason does not adequately explain the statement. Hence, the correct answer is option (d).
\[
\boxed{\text{The correct answer is option (d).}}
\]