Calculate the average atomic mass of sulfur.

The average atomic mass of a chemical element is calculated by taking into account the atomic masses of its naturally occuring isotopes and their respective abundances.

avg. atomic mass=∑i(isotopei×abundancei)

atomic masses of four isotopes of sulphur are

32S: 31.972 u→95.002%

33S: 32.971 u→0.76%

34S: 33.967 u→4.22%

36S: 35.967 u→0.014%

the average atomic mass of sulfur will be

Average atomic mass=31.972 u×0.95002+32.971 u×0.0076+33.967 u×0.0422+35.967 u×0.00014

Average atomic mass=32.063 u

it's c. elements are placed in rows based on how may valencies electrons have.