The atomic weight of `Cu` is `63.546`. There are only two naturally occurring isotopes of copper `.^(63)Cu` and `.^(65)Cu`. The natural abundance of the`.^(63)Cu` isotope must be approximately.

Explanation

Let the percentage of `.^(63)Cu=x` so, that of `.^(65)Cu=1-x.` Now, `63x+65(1-x)=63.5 rArr x=0.75`. This mean that the percentage of `.^(63)Cu=75%`