Digital electronics fundamentals: which logic gate is considered a universal gate because any other logic function can be implemented using only this gate (possibly with multiple stages and interconnections)?

Introduction / Context:
A universal gate is a building block from which any Boolean function can be constructed without needing any other gate types. In digital electronics, recognizing universal gates is essential for minimizing parts, simplifying procurement, and understanding functional completeness in logic design.

Given Data / Assumptions:

• The term “universal” means functionally complete: able to realize NOT, AND, OR, and by extension any combinational network.
• We consider basic gate families: AND, OR, EX-OR (XOR), and NAND.
• Gate availability is unrestricted; multiple stages and interconnections are allowed.

Concept / Approach:
NAND is universal because you can build a NOT gate by shorting its inputs (NAND(A, A) = NOT A). Using NOT plus NAND, you can form AND (by NAND followed by NOT) and OR (via De Morgan transforms). Once AND, OR, and NOT are available, all Boolean expressions can be implemented. NOR is also universal, but it is not one of the provided correct choices here; among the listed options, NAND is the universal gate.

Step-by-Step Solution:

Verification / Alternative check:
De Morgan’s laws and truth tables confirm the correctness of these equivalences. Many standard logic libraries offer NAND-only realizations as cost or speed optimizations, reinforcing universality.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing “universal” with “most commonly used.” Also, remembering NOR is universal does not negate NAND’s universality; both are universal, but you must select the one present among the options.

Final Answer:
NAND