Concept: The question tests on Percentage and comprehension of question and its inputs.
Liquid X =30% AND Water = 70%
8 Kg of Solution Y is taken and 2kg of Water evaporates from this.
=>8kg of Y has 30%of 8kg=2.4 kg of liquid X originally in it
2kg of Y that evaporated had 30% of 2kg or 0.6kg of liquid X in it.
The same is added back=>0.6 kg of liquid X that evaporated is added back to Y
Q. stem- We have to calculate the new percentage of liquid X in this solution(originally it was 30%)
This should be the "new" weight of liquid X in the solution/ Total weight of the solution *100
=2.4+0.6 / 8 =3/8 *100 = 37.5% (option c)