Detailed Instructions: In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Q: Problem: how many litres of pure acid are there in 10 litres of a 25 % solution 
Options: a ) 1.5 , b ) 1.6 , c ) 2.5 , d ) 1.8 , e ) 1.9
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
c