Exp. (c)The efficiency of Carnot engine isη=1−(T2​/T1​)where, T1​ is the temperature of the source and T2​ that of sink.Since, T1​T2​​=Q1​Q2​​So, η=1−Q1​Q2​​To obtain 100% efficiency (i.e., η=1 ), Q2​ must be zero i.e., if a sink at absolute zero would be available, all the heat taken from the source would have been converted into work.The temperature of sink means a negative temperature on the absolute scale at which the efficiency of engine is greater than unity. This would be a violation of the 2nd law of thermodynamics. Hence, a negative temperature on the absolute scale is impossible. Hence, we cannot reach absolute zero temperature.