Binary adders in digital design: A binary adder is a combinational logic circuit that can add how many binary numbers at a time?

Introduction / Context:
Binary adders implement arithmetic at the hardware level. The canonical adder (half adder/full adder and multi-bit versions) is designed to add two binary operands, producing a sum and a carry. Distinguishing how many numbers are added simultaneously clarifies adder use versus more complex arithmetic units like accumulators or multi-operand adders.

Given Data / Assumptions:

• A half adder adds two 1-bit inputs (A and B) producing sum and carry.
• A full adder adds A, B, and a carry-in but the carry-in is not a third independent operand; it is a chain signal.
• Ripple-carry and carry-look-ahead adders extend the bit width but still add two operands.

Concept / Approach:
Standard datapaths allocate two input buses to the adder: Operand X and Operand Y. The carry chain enables multi-bit addition but does not equate to adding a third independent number at the same time. Summation of three or more operands is handled by cascaded adders, carry-save adders, or tree structures (e.g., Wallace tree), not by a single basic adder that inherently accepts more than two numbers.

Step-by-Step Solution:
Identify the basic full adder inputs: A, B, and carry-in.Recognize that carry-in represents prior stage carry, not an independent operand.Conclude that a binary adder adds two numbers at a time.

Verification / Alternative check:
Examine ALU block diagrams: add instruction routes two register sources to the adder. Multi-operand sums use additional cycles or specialized adders.

Why Other Options Are Wrong:
“Hundreds/Thousands” are clearly incorrect; “One” misunderstands how addition requires at least two operands; “None” is invalid since a correct option exists.

Common Pitfalls:
Misinterpreting the carry-in as a third operand; confusing multi-cycle accumulation with single-cycle addition.

Final Answer:
Two.