Which element has an atomic weight approximately 36?

Which element has an atomic weight approximately 36?

• A. B C N O F (10, 12, 14, 16, 18)
• B. Cl (36)
• C. Na (23)
• D. H (1)

Answer: (B)

Atomic weight is the weighted average mass of an element’s atoms, taking into account the natural isotopic mix. Chlorine has two common isotopes, 35Cl and 37Cl, in roughly 75:25 abundance, which gives a weighted average around 35.5 amu, often rounded to 36. That makes chlorine the element with a mass near 36. The other options are much lighter: hydrogen is about 1 amu, sodium about 23 amu, and the group listed for the first set contains masses in the 10–18 range, far from 36.

Atomic weight is the weighted average mass of an element’s atoms, taking into account the natural isotopic mix. Chlorine has two common isotopes, 35Cl and 37Cl, in roughly 75:25 abundance, which gives a weighted average around 35.5 amu, often rounded to 36. That makes chlorine the element with a mass near 36. The other options are much lighter: hydrogen is about 1 amu, sodium about 23 amu, and the group listed for the first set contains masses in the 10–18 range, far from 36.