Afictitious element z has an average atomic mass of 223.06 u.223.06 u. element z has two naturally occuring isotopes. the more abundant isotope has an exact mass of 223.95 u223.95 u and a relative abundance of 65.51%.65.51%. calculate the exact mass of the second isotope.

221.37 u

Explanation:

The formula for the calculation of the average atomic mass is:

Given that:

For first isotope:

% = 65.51 %

Mass = 223.95 u

For second isotope:

Since the element has only 2 isotopes, so the percentage of second is 100 - first percentage.

% = 100 %  - 65.51 %  = 34.49 %

Let, Mass = x u

Given, Average Mass = 223.06 u

Thus,  

Solving for x, we get that:

x = 221.37 u

Thus mass of second isotope = 221.37 u

a electronegativity decreases beacuse the size of nucleus is bigger.