Assertion–Reason (DC choppers): A class C chopper (two-quadrant) can operate in the first and second quadrants. Reason: A class B chopper operates only in the second quadrant (regenerative quadrant). Select the correct option.

Introduction / Context:
DC choppers are classified by the quadrant(s) in which the voltage–current pair (V, I) operates. Understanding quadrant operation clarifies power flow and regenerative capability. This question checks knowledge of Class B and Class C choppers and their quadrant behavior.

Given Data / Assumptions:

• Class B chopper: second-quadrant operation (V > 0, I < 0), energy returns to the source.
• Class C chopper: combination of Class A and B choppers.

Concept / Approach:
Class C is effectively a two-quadrant chopper combining Class A (first quadrant: motoring) and Class B (second quadrant: regenerative braking), enabling current reversal or power flow back to source depending on load and control.

Step-by-Step Solution:
1) Class B chopper permits energy to flow from load to source with V positive and I negative.2) Class C chopper is a combination of Class A and Class B, hence supports both first and second quadrants.3) Therefore, the reason directly supports the assertion.
Verification / Alternative check:
Standard chopper classification charts show Class C = A + B (two-quadrant operation).

Why Other Options Are Wrong:

• Options stating R is not the explanation are incorrect because knowledge of Class B behavior explains why Class C covers both quadrants.
• Options claiming A or R is wrong contradict accepted definitions.

Common Pitfalls:

• Confusing Class C with Class D (third and fourth quadrants).
• Assuming Class B allows forward current; it does not.

Final Answer:
Both A and R are correct and R correctly explains A.