1. calculate the volume of concentrated HNO_3 (68%)that is needed to prepare stock solution 0.25M in 1000mL volumetric flask. (density HNO_3 = 1.513 g/cm^3)

2. from above stock solution, determine volume needed to dilute to 500mL volumetric flask that contained 10 times dilution.

See your post above. After seeing how to do the first part you should be able to do the second part.