Write the chemical names of two salts belonging to the sodium family.

$(a)$ What is a universal indicator?
$(b)$ Write the chemical equation involved in the preparation of sodium hydroxide. Name the process.

$A$ metal carbonate $X$ on reacting with an acid gives a gas which when passed through a solution $Y$ gives the carbonate back. On the other hand,a gas $G$ that is obtained at anode during electrolysis of brine is passed on dry $Y$,it gives a compound $Z$,used for disinfecting drinking water. Identify $X$,$Y$,$G$ and $Z$.

What is the molarity of a solution prepared by dissolving $8 \ g$ of $NaOH$ in water to make a total volume of $100 \ mL$ (in $M$)?

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

$A$ sulphate salt of a Group $2$ element of the Periodic Table is a white,soft substance,which can be moulded into different shapes by making its dough. When this compound is left in the open for some time,it becomes a hard solid mass and cannot be used for moulding purposes. Identify the sulphate salt and explain why it shows such behavior. Provide the chemical reaction involved.