The melting points of most of the solid substances increases with an increase of pressure acting on them. However, ice melts at a temperature lower than its usual melting point, when the pressure increases. This is because:

Which of the following statements about hydrogen is/are correct?

I. Hydrogen has three isotopes of which protium is the most common.

II. Hydrogen ion $\left({\mathrm{H}}^{+}\right)$ exists freely in solution.

III. Dihydrogen ${\mathrm{H}}_2$, acts as a reducing agent.

Select the correct answer using the codes given below:

Consider the following statements.

I. Metals are generally hard.

II. Mercury is hard in nature and is not poisonous.

III. Mercury usually enters human food chain from aquatic animals.

Which of the statement(s) is/are correct?