In a basic aqueous solution,if the concentration of $[OH^-]$ decreases,what happens to the $pH$?

Salt $A$,commonly used in bakery products,on heating gets converted into another salt $B$,which itself is used for the removal of hardness of water,and a gas $C$ is evolved. The gas $C$,when passed through lime water,turns it milky. Identify $A$,$B$,and $C$.

Write the balanced chemical equations for the following reactions:
$(a)$ Chlorine is passed over dry slaked lime.
$(b)$ Sodium bicarbonate reacts with dilute hydrochloric acid.
$(c)$ Sodium bicarbonate is heated.

Which of the following gives the correct increasing order of acidic strength?

The metal salt $A$ is blue in colour. When salt $A$ is heated strongly over a burner,a substance $B$ present in it is eliminated and a white powder $C$ is left behind. When a few drops of a liquid $D$ are added to powder $C$,it becomes blue again.
$(a)$ Identify $A, B, C, D$.
$(b)$ Write the chemical equations involved.
$(c)$ Give an example of a salt which also shows the above property.

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