12.5 ml of solution conatiing 6 gm of dibasic cid in 1 Lt was found to be neutralised by 10 ml of a decinormal solution of NaOH, then the moecular mass of acid is ??

Amount of acid in 1L (1000 ml) solution = 6 g
Amount of acid in 12.5 ml solution = (6/1000) x 12.5 g
  = 0.075 g
At neutralisation,
10 ml of N/10 NaOH $\equiv$10 ml N/10 acid
Now,
10 ml N/10 acid = 0.075 g
So, 1000 ml N/10 acid = (0.075/10) x 1000
  = 7.5 g
  1000 ml of N acid = 7.5 x 10 = 75 g

Thus the equivalent mass of acid = 75
So, molecular mass = 75 x 2 = 150 g  ( since the acid is dibasic).