10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be (a) 4 ml (b) 8 ml (c) 12 ml (d) 16 ml

The answer is option (d) 16ml.

10 ml of NaOH requires 8 ml of HCl, and 20 ml of NaOH requires 8 x 2 = 16 ml of HCl.