What is the atomic weight of hydrogen?

The atomic weight of hydrogen is approximately 1.008, which is generally rounded to 1 for simplicity in many contexts. This value represents the average mass of hydrogen atoms considering the abundance of its isotopes, primarily protium, which has one proton and no neutrons.

Option B, suggesting an atomic weight of 2, likely confuses hydrogen with its isotope deuterium, which contains one proton and one neutron. While deuterium is indeed heavier than ordinary hydrogen and has an atomic weight near 2, it is not the atomic weight of hydrogen itself.

The other choices—3 and 4—do not represent the atomic weight of hydrogen or any of its stable isotopes. The values significantly exceed the actual atomic weight of hydrogen, making them incorrect in this context. Thus, the accepted atomic weight of hydrogen is closest to 1.