i finally got it.....i think !

formulae mass: 56moles so 16.0g in 56 = 0.286mol

moles = volume x concentration

0.286 x 25 / 1000 = 7.15 x 10^-3 = 0.00715 for potassium hydroxide

0.05 x 50 / 1000 = 2.5 x 10 ^-3 = 0.0025 for sulphuric acid

0.0025 x 2 = 5 x 10 ^-3 = 0.005

so, 0.005 /0.00715 x 100 = 69.9 = 70%

hope it is correct, if yes thanks for the guideness..