Which ions are produced when caustic soda undergoes ionization in water?

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.

Write true or false for the following statement:
The process of dissolving an acid or a base in water is a highly exothermic process.

Give suitable reasons for the following statements: An aqueous solution of sodium chloride is neutral,but an aqueous solution of sodium is basic.

Which of the following metals reacts with sodium hydroxide to produce a salt and $H_2$ gas?