Definition of a full adder: A full adder stage adds two single-bit operands along with an incoming carry (Cin) and produces a Sum and a carry-out (Cout). What does a full adder add?

Introduction / Context:
A full adder is the fundamental building block for multi-bit ripple-carry adders. Understanding its inputs clarifies how larger adders are constructed by cascading stages.

Given Data / Assumptions:

• Single full-adder cell, not a 4-bit adder IC.
• Inputs: A (1 bit), B (1 bit), Cin (1 bit).
• Outputs: Sum (1 bit), Cout (1 bit).

Concept / Approach:
The full adder solves a three-input addition problem at the bit level. The logic implements the equations Sum = A XOR B XOR Cin and Cout = majority(A, B, Cin), enabling carry propagation from less significant bits to more significant bits in a ripple chain.

Step-by-Step Solution:

Verification / Alternative check:
Truth tables confirm that for all 8 combinations of A, B, Cin, the Sum/Cout match binary addition rules.

Why Other Options Are Wrong:
Options referring to “2-bit” or “4-bit” numbers confuse a single full-adder cell with multi-bit adder ICs that contain several full-adder stages.

Common Pitfalls:
Mixing up half adder vs full adder; a half adder lacks Cin and cannot be directly cascaded for accurate multi-bit addition with carry propagation.

Final Answer:
two single bits and one carry bit