4g of copper was dissolved in conc. HNO _ 3 . The copper nitrate...

$4g$ of copper gave $5g$ of its oxide means,

$1g$ of oxygen combine with $4g$ of copper.

$∵$ Eq. wt of oxygen $= 8$,

Therefore,

$8g$ of oxygen combine with $= 4 \times 8g$ of copper $= 32g$

Hence,

Equivalent weight of copper $= 32$