To solve this problem, we need to consider that the final mixture should contain 25% alcohol. This means that the alcohol should make up 25% of the total volume of the mixture.

We are given that we have 75 ml of alcohol. To find out how much water should be added, we can set up a proportion using the volume of alcohol and the total volume of the mixture.

Let`s assume that x ml of water needs to be added. According to the proportion:

75 ml (volume of alcohol) / (75 ml + x ml) (total volume of mixture) = 25% / 100%

Simplifying the proportion, we get:

75 / (75 + x) = 1 / 4

To get rid of the fractions, we can cross multiply:

4 * 75 = 1 * (75 + x)

300 = 75 + x

Subtracting 75 from both sides gives us:

225 = x

Therefore, the correct answer is option 2, which states that 225 ml of water needs to be added to the 75 ml of alcohol to obtain a mixture containing 25% alcohol.