Heat Transfer
The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K₀ + at. where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be

W/m.k²
None, A is just a number
W/m
W/m.k

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Heat Transfer
The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are

(COP)R = 2.5; (COP)HP = 1.5
(COP)R = (COP)HP = 0.6
(COP)R = 1.5; (COP)HP = 2.5
(COP)R = (COP)HP = 2.5

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