The atomic mass of element is numerically euqal to the mass of 1 mole of its atoms. Since 1 mole of atoms is `6.022 xx 10^(23)` atoms, so it means that the atomic mass of an element is numerically equal to the mass of its `6.022 xx 10^(23)` atoms.
Now, `1` atom of element X has mass `= 2.65 xx 10^(-23) g`
So, `6.022 xx 10^(23)` atoms of element X have mass `= 2.65 xx 10^(-23) xx 6.022 xx 10^(23)`
`= 15.96 g`
`= 16 g`
Thus, the atomic mass of the element X is 16 u. The element of atomic mass 16 u is oxygen, having the symbol O.
