KOH :
M1 = 0.1 M
V1 = ?
HCl :
pH = 2.25
pH = -log [H+] = -log M2
-log M2 = 2.25
log M2 = -2.25
M2 = 10^(-2.25) = 0.00562
V2 = 300 ml
We know that,
M1V1 = M2V2
0.1×V1 = 0.00562×300
V1 = (0.00562×300)/0.1
V1 = 1.686/0.1
V1 = 16.86 ml.
i.e 16.86 ml of KOH is required.