**Q1: **

Chlorine has two stable isotopes, and ,
with atomic masses 34.9689 u
and 36.9659 u respectively.
The relative abundance of in an average sample of chlorine is
.

Calculate the average absolute abundance of .

Calculate the average atomic mass of chlorine.

**Q2: **

Gallium has two stable isotopes, and , with atomic masses 68.9256 u and 70.9247 u respectively.

Calculate, to 3 significant figures, the abundance of for a sample of gallium with an average atomic mass 69.723 u.

Calculate, to 3 significant figures, the abundance of for a sample of gallium with an average atomic mass of 69.620 u.

**Q3: **

Magnesium has three stable isotopes, , ,
and ,
with atomic masses 23.9850 u,
24.9858 u, and
25.9826 u respectively.

The natural abundances of and
are and respectively.
Calculate the average atomic mass of magnesium.

The relative abundances of magnesium isotopes in a sample are
and .
Calculate, to 4 significant figures, the absolute abundance of in the sample.