Equal lengths of magnesium ribbon are taken in two test tubes $A$ and $B$. $H_{2}SO_{4}$ is added to test tube $A$ and $H_{2}CO_{3}$ in test tube $B$ in equal amounts.
$(a)$ Identify the test tube showing vigorous reaction.
$(b)$ Give reason to support your answer.
$(c)$ Name the gas liberated in both the test tubes. How will you prove its liberation?

Calcium phosphate is present in tooth enamel. Its nature is:

$(a)$ Write the chemical formula of hydrated copper sulphate and anhydrous copper sulphate. Giving an activity,illustrate how these two are interconvertible.
$(b)$ Write the chemical names and formulae of Plaster of Paris and gypsum.

What is the $pOH$ value of a $10^{-4} \; M$ aqueous solution of $HCl$?

$(a)$ Give the chemical names of acids present in:
$(i)$ ants
$(ii)$ lemon
$(iii)$ milk
$(iv)$ tomato

Answer the following:
$(i)$ Why is Plaster of Paris written as $CaSO_{4} \cdot 1/2 H_{2}O$? How is it possible to have half a water molecule attached to $CaSO_{4}$?
$(ii)$ Why is sodium hydrogen carbonate an essential ingredient in antacids?
$(iii)$ When electricity is passed through an aqueous solution of sodium chloride,three products are obtained. Why is the process called chlor-alkali?