The number of neutrons in the most common isotope of hydrogen is:

0

The correct answer is Option (3) → 0

The most common isotope of hydrogen is protium (¹H or hydrogen-1), which has:

• 1 proton
• 0 neutrons
• 1 electron

It accounts for over 99.98% of naturally occurring hydrogen.

The other isotopes are deuterium (¹H₂, 1 neutron, rare) and tritium (¹H₃, 2 neutrons, trace and radioactive).

Thus, the number of neutrons in the most common isotope is 0.