Sodium carbonate is a basic salt because it is a salt of :

Dry $HCl$ gas does not change the colour of dry blue litmus. Give reason.

If the approximate $pH$ of a solution is $7,$ what will be the colour of $pH$ paper when dipped into that solution?

Explain why:
$(a)$ the colour of copper sulphate crystals changes on heating?
$(b)$ baking soda acts as an antacid?
$(c)$ an acid should be added to water while diluting?

Which gas is evolved when dilute hydrochloric acid reacts with zinc? Write the molecular formula of this gas.

State the number of water molecules present in crystals of washing soda and Plaster of Paris. What are these water molecules called?