Adder basics in digital electronics: A full adder takes _____ input bits and produces a SUM and a _____ output.

Introduction / Context:
The full adder is a fundamental combinational block used to construct multi-bit adders. Unlike the half adder, which adds two bits, the full adder adds two operand bits and a carry-in, producing a sum and a carry-out. This behavior allows chaining many stages to create ripple-carry or more advanced adders.

Given Data / Assumptions:

• Inputs: A, B (operand bits), and Cin (carry-in) → total 3 input bits.
• Outputs: SUM and Cout (carry-out).
• Standard Boolean implementation is assumed.

Concept / Approach:
Equations for a full adder are: SUM = A ⊕ B ⊕ Cin; CARRY = (A * B) + (Cin * (A ⊕ B)). This allows a per-bit computation that propagates carry to the next significant bit.

Step-by-Step Solution:
Recognize the distinction: half adder (2 inputs) vs. full adder (3 inputs including Cin).Recall outputs: SUM and CARRY.Therefore, select “3, CARRY.”

Verification / Alternative check:
Standard logic diagrams show the carry chain connecting Cout of bit i to Cin of bit i+1.

Why Other Options Are Wrong:
(a) and (c) are nonsensical pairings; (d) cannot be true because the others contradict full-adder behavior.

Common Pitfalls:
Misinterpreting carry-in as a separate operand; it is a chain input, but it makes the total input bit count three.

Final Answer:
3, CARRY.