Common emitter is the only one of the three configurations that gives gain greater than unity in all three quantities — voltage, current and power — which is exactly why it is the standard amplifier stage. The answer is i, ii, iii, option 2.

Why power gain follows automatically. Power gain is the product of the other two,

\(A_{P}=A_{V}\times A_{I}\)

so a configuration with high voltage and high current gain necessarily has the largest power gain of the three — typically 30 to 40 dB. Common base amplifies voltage but not current; common collector amplifies current but not voltage; only common emitter does both, so its power gain is unmatched.

Why statement iv is false, and this is the discriminator. The CE stage is the least stable of the three. Two effects work against it:

Thermal. Its high current gain amplifies the leakage current \(I_{CBO}\) as well as the signal —

\(I_{CEO}=(1+\beta)I_{CBO}\)

— and since leakage roughly doubles for every 10 °C rise, the operating point drifts with temperature and can run away without stabilising feedback.

Frequency response. The 180° phase inversion means the collector-base capacitance is multiplied by the voltage gain when referred to the input — the Miller effect, \(C_{in}=C_{bc}\left(1+|A_{V}|\right)\) — which loads the source heavily and gives the CE stage the poorest high-frequency performance of the three. Common base, having no inversion and no Miller multiplication, is the configuration used at high frequencies for precisely this reason.

The remedy in practice is voltage-divider bias with an emitter resistor, whose negative feedback holds the operating point steady against both temperature and the wide spread of \(\beta\) between devices. Stability is therefore something the CE stage must be given by its bias network, not something the configuration provides.

Hence, the correct statements are i, ii and iii.