Step 1: Analyze the Assertion (A)
Assertion (A): The deflection of a compass needle placed near a current-carrying wire decreases when the magnitude of an electric current in the wire is increased.
This statement is false. An increase in electric current strengthens the magnetic field around the wire, causing the compass needle's deflection to increase, not decrease.
Step 2: Analyze the Reason (R)
Reason (R): Strength of the magnetic field at a point due to a current-carrying conductor increases on increasing the current in the conductor.
This statement is true. The magnetic field strength is directly proportional to the current in the wire.
Step 3: Relationship between Assertion and Reason
The reason is true, but it does not explain the false assertion.
Final Answer:
(A) is false, but (R) is true.