Answer:
c. 50%
Step-by-step explanation:
The maximum efficiency of a heat engine is:
η = 1 − (Tc / Th)
where Tc is the low temperature and Th is the high temperature.
In this case, Tc = 300 K and Th = 600 K:
η = 1 − (300 / 600)
η = 0.50
The maximum possible efficiency is 50%.