How many molecules are in 2.50 moles H2SO4?

Remember M1V1=M2V2. (M is for molarity. V is for volume.)

So:
0.25M x V1 = 0.50 M x 0.050 L


V1 = 0.50 M x 0.050L / 0.25 M = 0.1 L


Wait! You need it in mL so 0.1 L x 1000 = 100 mL