Question

What volume of water should be added to 50mL of HNO3 having density 1.5g/male and 63% by weight to have one molar solution

Answer 1

Mass of HNO3 solution = 50 mL * 1.5 g/mL 
Mass of HNO3 = mass of HNO3 solution * 0.63 

Convert mass of HNO3 to moles for molarity, concentration = moles / volume. 
Concentration : 1 mole/L per the problem. You just worked out the moles of HNO3. Calculate the volume of the solution. 

Volume of water = volume of solution from above - 50 mL