If the resistance $R_1$ is increased (see figure), how will the readings of the ammeter and voltmeter change?

(A-D) In the given common emitter transistor circuit, the input circuit consists of the base-emitter junction with resistance $R_1$.
When $R_1$ is increased, the base current $I_B$ decreases according to Ohm's law $(I_B = V_{in} / R_1)$.
The output collector current $I_C$ is related to the base current by the relation $I_C = \beta I_B$, where $\beta$ is the current gain of the transistor.
Since $I_B$ decreases, the collector current $I_C$ also decreases.
The ammeter is in series with the collector, so its reading decreases.
The voltmeter is connected across the resistor $R_2$ in the output circuit. The voltage across $R_2$ is given by $V_{out} = I_C R_2$.
As $I_C$ decreases, the voltage drop $V_{out}$ across $R_2$ decreases.
Therefore, the readings of both the ammeter and the voltmeter will decrease.