Sulagna,

The original mixture has an acid to water ratio of 1:24. Thus 25 units of this mixture would be 1 unit of acid and 24 units of water. If you now take these 25 units and mix them with water in the ratio of 1:3 then you would need 3 × 25 = 75 units of water. This would make a final volume of 25 + 75 = 100 units of solution made up of 1 units of acid and 24 + 75 = 99 units of water. For the final volume to be 200 ml each unit would need to be 2 ml and hence the 1 unit of acid is 2 ml.

Penny