Explanation:

- Hydrogen is the lightest element and consists mainly of one proton in its nucleus.

- The approximate atomic mass of hydrogen is 1 unified atomic mass unit (u).

- This is because each proton has an approximate mass of 1 u, and hydrogen has no neutrons in its common isotope.

- Therefore, hydrogen is significantly lighter compared to elements like carbon or oxygen.

- Option:1, 12 u is the atomic mass of carbon, not hydrogen.

- Option:2, 4 u, is the atomic mass for helium, not hydrogen.

- Option:3, 1 u, correctly represents hydrogen's atomic mass.

- Option:4, 14 u relates to elements like nitrogen, not hydrogen.

Option:3 – 1 is the correct answer.