The number of moles of nitric acid can be obtained by multiplying the molarity with volume M×V= Moles of HNO3=1000250×2=0.5
The mass of nitric acid can be obtained by multiplying the number of mols with molar mass and dividing with percentage concentration. ∴HNO3 required =0.5×63×70100=45g
Thus 45.0g conc. HNO3 of concentrated nitric acid solution should be used to prepare 250mL of 2.0MHNO3.