How many mL of 2m Hbr are needed to exactly neutralize 20 mL of 4m KOH?

= 40 mL

Explanation:

Using the dilution formula;

M1V1 = M2V2

where M1 is the initial concentration, V1 is the initial volume, M2 is the concentration attained while V2 is the new volume.

Therefore; To get the new volume;

V2 = M1V1/M2

= (20mL * 4 M) / 2 M

= 40 mL