Question

# Chemical formula of washing soda is:a.) $N{a_2}C{O_3}$b.) $N{a_2}C{O_3}.10{H_2}O$c.) $N{a_2}C{O_3}.5{H_2}O$d.) $N{a_2}S{O_4}.10{H_2}O$

Hint: Try to recall that washing soda is a white crystalline solid which exists as decahydrate and on heating, the decahydrate loses the water of crystallisation and changes to a white powder called soda ash. Now by using this you can easily find the correct option from the given options.

Complete step by step solution:
-It is known to you that washing soda is a white crystalline solid which exists as a decahydrate and is readily soluble in water.
-It reacts with dilute mineral acids evolving carbon dioxide.
-Also, it gets hydrolysed by water to form an alkaline solution.
-On strong heating, it loses all its water of crystallisation and becomes completely anhydrous and changes to white powder called soda ash.
-Now, since it is known to you that $N{a_2}C{O_3}$ is soda ash. So, you can easily say that $N{a_2}C{O_3}.10{H_2}O$ is the chemical formula of washing as it is the hydrated form of soda ash.
Therefore, from above we can say that option B is the correct option for the given question.