Strength of acid depends on the ability of the compound to donate the proton and the number of protons it can donate in the solution. Among all the given acids ${\text{H}}_2{\text{SO}}_4$ has maximum ability to donate $H^{+}$ in the aqueous solution. Also, ${\text{H}}_2{\text{SO}}_4$ can donate two $H^{+}$ ions per molecule while all other acids can donate only one $H^{+}$ ion in the solution. Hence, ${\text{H}}_2{\text{SO}}_4$ is the strongest acid among the given acids.

Acids react with metals to produce the respective metal salt along with hydrogen gas. The general form of the reaction is given below:
$\text{Acid (aq)}+\text{Metal (s)}\to \text{Salt (aq)}+\text{Hydrogen (g)}$
For example:
When hydrochloric acid reacts with zinc, it produces zinc chloride along with the evolution of hydrogen gas.
The chemical reaction is given below:
$2\text{HCl (aq)}+\text{Zn (s)}\to {\text{ZnCl}}_2\text{(aq)}+{\text{H}}_2\text{(g)}$

pH indicators are aqueous solutions of either weak acids or weak bases. They are chemical detectors of hydrogen ions ($H^{+1}$) and hydroxide ions ($O{H}^{-1}$) . It is added in small quantity to a solution to determine the pH.

Gastric juices that are released in the stomach are acidic in nature. Thus, their pH is less than seven. When they are released in excess quantity, we take mild bases like baking soda to neutralise its effect.

Metallic oxides with both acidic and basic character are called amphoteric oxides. They act as either acid or a base in a neutralisation reaction to form salt and water.

E.g., ${\text{Al}}_2{\text{O}}_3,\text{ZnO}$