The output characteristics of a transistor in CE mode is the graph...

In common emitter (CE) configuration, the input is applied between the base and emitter, and the output is taken across the collector and emitter.

The output characteristics of a transistor represent the variation of the output current with the output voltage, keeping the input current constant.

For a CE transistor, the output current is the collector current $I_C$, the output voltage is the collector-emitter voltage $V_{CE}$, and the input current is the base current $I_B$.

Therefore, the output characteristics are obtained by plotting $I_C$ against $V_{CE}$ at constant $I_B$.

Answer: $I_C$ against $V_{CE}$ at constant $I_B$