In 100 g of a 63% solution of nitric acid, 20 g of copper was dissolved. The volume of the evolved gas is equal.

Reaction of nitric acid with copper.
2HNO3 + Cu = Cu (NO3) 2 + H2.
Determine the mass of the acid in the solution.
m (HNO3) = W (HNO3) • m (solution) / 100% = 63% • 100 g / 100% = 63 g.
Find the number of moles of nitric acid and copper.
n (HNO3) = m / Mr = 63 g / 2 • 63 g / mol = 0.5 mol.
n (Cu) = 20 g / 64 g / mol = 0.3 mol.
The acid will be in excess, so the calculation of the volume of hydrogen is based on copper.
V (H2) = n • Vm = 0.3 mol • 22.4 mol / L = 6.72 L.