I believe your answer is 23.

Credit: answers.yahoo.com

Hope this helps!

Option 1/A (It is the first one)

**Answer:**

compound is formed .............

** = 24.3
**

The average atomic mass of X is the <em>**weighted average**</em> of the atomic masses of its isotopes.

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

Thus,

0.790 × 24 u = 18.96 u

0.100 × 25 u = 2.50 u

0.110 × 26 u = <u>2.86 u</u>

TOTAL = 24.3 u

∴ The relative atomic mass of X is **24.3**.