Correct Option: B

Given P_{D Max} = 2.5 Watts
P_oac =?
We know maximum efficiency of direct coupled class-A amplifier is 50% i.e., η = 50%

η = 50% = 0.5 =	Po(ac)
	Pi(dc)

∴ P_{i (dc)} = P_{o (ac)} + P_D) P_{i (dc)}
= P_{o (ac)} + 2.5

or 0.5 =	Po(ac)
	Po(ac) + 2·5

or 0.5P_o(ac) + 1.25 = P_{o (ac)}
or 0.5 P_{o (ac)} = 1.25

or Po (ac) =	1·25	= 2.5 watts.
	0·5

where, P_{o (ac)} = output ac power to the load
P_{i (dc)} = input dc power to the transistor