Element R has three isotopes. The isotopes are present in 0.0825, 0.2671, and 0.6504 relative abundance. If their masses are 98.18, 110.65, and 140 respectively, calculate the atomic mass of element R.

The relative atomic mass of R = 128.71

Explanation:

The relative atomic mass of an element which exhibits isotopy is the average mass of its various isotopes as they occur naturally in any quantity of the element.

Therefore, the relative atomic mass of element R is calculated thus;

Relative atomic mass = sum (relative abundance of each isotope * atomic mass of isotope)

= (0.0825 * 98.18) + (0.2671 * 110.65) + (0.6504 * 140)

= 8.099 + 29.554 + 91.056

= 128.71

Therefore, the relative atomic mass of element R is 128.71