How many ml of 0.250 m h2so4 is required to completely react with 25.0 ml of 1.50 m naoh?

Best   Because the equation is this: MaVa = MbVb 
Ma = Molarity of H+ ions 
Va = Volume of acid solution in mL 
Mb = Molarity of OH- ions 
Vb = Volume of base solution in mL 

Since H2SO4 is a diprotic base (two hydrogens), then one mol of H2SO4 will disassociate into two H+ ions 
Therefore in the equation you must double the molarity of H2SO4, because the formula doesn't ask for the molarity of the acid, it asks for the molarity of H+ ions. 

Therefore: 
Ma×Va = Mb×Vb 
(0.5 M)× Va = (0.25 mL)×(1.5M) 
Va = Mb×Vb / Ma 
Va = 0.75 mL