Correct answer: 90 J
The efficiency of the Carnot engine is given as 1/10, which means the ratio of work done to heat absorbed is 1/10. When used as a refrigerator, the heat absorbed (Q2) from the lower reservoir is given by Q2 = W / (1 - efficiency). Substituting W = 10 J and efficiency = 1/10, we get Q2 = 10 / (1 - 1/10) = 10 / (9/10) = 90 J.