Equal volumes of hydrochloric acid and sodium hydroxide solutions of the same concentration are mixed. The $pH$ of the resulting solution is checked with a $pH$ paper. What would be the colour obtained? (You may use the colour guide given in the figure.)

$(i)$ Name the products obtained in the chlor-alkali process.
$(ii)$ Name the gases liberated at the anode and at the cathode,respectively.
$(iii)$ Name the solution which is used as raw material in this process.

Which salt solution has a $pH$ greater than $7$?

What will be the $pH$ of an aqueous solution of $NH_{4}Cl$?

Which of the following is a strong acid?

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.