
$1.$ efficiency more than $27 \%$
$2.$ efficiency less than the efficiency a Carnot engine operating between the same two temperatures.
$3.$ efficiency equal to $27 \%$
$4.$ efficiency less than $27 \%$
$S1:$ The efficiency of a heat engine can be $1,$ but the coefficient of performance of a refrigerator can never be infinity.
$S2:$ The first law of thermodynamics is basically the principle of conservation of energy.
$S3:$ The second law of thermodynamics does not allow several phenomena consistent with the first law.
$S4:$ A process,whose only result is to transfer heat from a colder to a hotter object, is impossible.