Which statement best explains why hydrogen’s atomic number is equal to its mass?

Question

hydrogen is in the first row and first column of the periodic table
hydrogen is stable, with two electrons in its outer shell
hydrogen only has one electron
hydrogen does not have any neutrons

Answer 1

The statement that best explains why hydrogen’s atomic number is equal to its mass is:

hydrogen does not have any neutrons.

Hydrogen has one proton and typically one electron, giving it an atomic number of 1. It has no neutrons in its most common isotope (protium), which gives it an atomic mass of approximately 1. Therefore, its atomic number (1) equals its mass number (1) when considering this isotope.