due to which compound salt get wet in rainy season ?

Answer 1

I think there may be a typo in your question. I will take a stab at it anyway.

The relative humidity is the measure of water present in the air. During the rainy season the RH = 100%. The salt will hygroscope moisture from the air since the air has higher moisture content than the salt.

** If you put a few grains of rice in the salt, it will prevent the salt from hygroscoping so much that it clumps and fails to flow. **