Which gas is evolved when dilute hydrochloric acid reacts with zinc? Write the molecular formula of this gas.

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.)

The chemical formulas for Gypsum and Plaster of Paris are,respectively:

Explain the action of dilute hydrochloric acid on the following with chemical equations:
$(a)$ Magnesium ribbon
$(b)$ Sodium hydroxide
$(c)$ Crushed egg shells

Which of the following is acidic in nature?

Which of the following is(are) true when $HCl(g)$ is passed through water?
$(i)$ It does not ionise in the solution as it is a covalent compound.
$(ii)$ It ionises in the solution.
$(iii)$ It gives both hydrogen and hydroxyl ion in the solution.
$(iv)$ It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule.