For a transistor to be used as an amplifier,which of the following conditions must be satisfied?

When a transistor is used as an amplifier in common emitter configuration,which of the following statements are correct?
$(1)$ The base-emitter junction is forward-biased.
$(2)$ The base-emitter junction is reverse-biased.
$(3)$ The input signal is connected in series with the biasing voltage to the base-emitter junction.
$(4)$ The input signal is connected in series with the biasing voltage to the base-collector junction.

In the given transistor circuit,the base current is $35 \mu A$. The value of $R_b$ is.....$k\Omega$.

In common emitter mode of a transistor, the d.c. current gain $(\beta)$ is $20$, and the emitter current $(I_E)$ is $7 \text{ mA}$. The collector current $(I_C)$ is:

$A$ transistor is operating in the active mode. $v_1$ is the potential barrier across the base-emitter junction and $v_2$ is the potential barrier across the collector-base junction. $b_1$ is the width of the depletion layer of the base-emitter junction and $b_2$ is the width of the collector-base junction.

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $n-p-n$ transistor permits more current than a $p-n-p$ transistor.
Reason $R$: Electrons have greater mobility as a charge carrier.
Choose the correct answer from the options given below: