A

In a common emitter transistor configuration, the alternating current gain, denoted as β (beta), quantifies how much the collector current (I_C) changes in response to a change in the base current (I_B).
Here is the detailed explanation:
Step 1: The formula for current gain β in a common emitter arrangement is defined as follows:
$$ \beta = \frac{\Delta I_C}{\Delta I_B} $$
where:

• \(\Delta I_C\) is the change in collector current.
• \(\Delta I_B\) is the change in base current.

Step 2: Hence, the gain parameter (β) expresses that for every unit change in the base current (I_B), there is a β unit change in the collector current (I_C), independent of other voltages and conditions in the circuit.
Final Conclusion: Thus, option (A) presents the correct expression for the alternating current gain β in a common emitter arrangement.
Therefore, the answer is (A).