A solution mass of 1 kg is 10 times greater than 100 g, thus one kilogram (1 kg) of a 2.5% KI solution would contain of KI.

The answer is " ... one kilogram of a 2.5% KI solution would contain 25 grams of KI."

Explanation:

A 2.5% by mass potassium iodide KI solution is equal to 2.5 grams of KI divided by 100 grams of the KI solution and then multiply by 100, that is

2.5% by mass = [2.5grams KI / (100grams KI solution) ] * 100

We multiply the mass of the solute and the mass of the solution by 10 each so that 100 grams becomes 1000 grams.

2.5% by mass = [ (2.5grams KI * 10) / (100grams KI solution * 10) ] * 100 = (25grams KI / 1000grams KI solution) * 100

Since 1000 grams is equal to 1 kg, the expression becomes

2.5% by mass = (25grams KI/1kg KI solution) * 100

The expression above shows that a 2.5% by mass KI solution would contain 25 grams of potassium iodide in 1 kilogram KI solution.