Question

The chemical equivalent of copper relative atomic mass 63.5 is 63.5 g.

Answer 1

Naturally occurring copper consists of $69.2\%$ copper-$63{(}^{63}Cu)$ and $30.8\%$ copper-$65{(}^{65}Cu)$

Still think in terms of $100$ atoms and don't be put off by decimal fractions, it still works out correctly because $69.2+30.8=100$

average mass = relative atomic mass of copper = $\frac{(63\times 69.2)+(65\times 30.8)}{100}=63.5g$