\(=0.5\) moles No. of moles \(=\) molarity \(\times\) volume

Requird mass of \(\mathrm{HNO}_{3}=0.5 \times 63\)

\(=31.5 \mathrm{gm}\)

\(70 \mathrm{gm}\) of \(\mathrm{HNO}_{3}\) are present in \(100 \mathrm{gm}\) of solution,

So \(1\; gm\) will be present in \(100 / 70 \mathrm{gm}\) of solution.

\(31.5 \mathrm{gm}\) be present in \((100 / 70) \times 31.5 \mathrm{gm}\) of solution

\(=45 \;\mathrm{gm}\)