Question

what happens when crystalline sodium carbonate,is kept exposed to air? explain with help of chemical equation? write names of product obtained

Answer 1

A process called efflorescence happens. Na2CO3 loses its water of crystallization and turns to white powder.
  Na2Co3 . 10H2O -------> Na2CO3 + 10 H20 (evaporates)

Answer 2

Explanation:

Sodium carbonate is a water soluble salt of sodium. Crystalline sodium carbonate, on keeping, loses its water of crystallization readily and a white powder is obtained. This powder is called washing soda

Na2Co3. 10H2O

Na2CO3. H2O+9H2O