Question

FIRST ANSWER = BRAINLIEST

Answer 1

$A_{r}$ = 24.3

The average atomic mass of X is the weighted average of the atomic masses of its isotopes.  

We multiply the atomic mass of each isotope by a number representing its relative importance (i.e., its % abundance).  

Thus,  

0.790 × 24 u = 18.96 u

0.100 × 25 u =   2.50 u

0.110 × 26 u =    2.86 u  

       TOTAL =  24.3   u

∴ The relative atomic mass of X is 24.3.