The formula of soda ash is
(a) Na2CO3.10H2O (b) Na2CO3.2H2O
(c) Na2CO3.H2O (d) Na2CO3
Answer: (d) Na2CO3
On heating washing soda, it loses its water of crystallisation, above 373 K, it becomes completely anhydrous white powder called soda ash.
Na2CO3.10H2OWashing Soda373 K<−−−−→Na2CO3Soda ash+10H2O