Which logic gate is used to represent a Product of Sum (POS) expression?

A Boolean expression is in Product of Sum (POS) form when it is a logical product (AND) of several sum terms, where each sum term is itself a logical sum (OR) of literals — for example, (A + B) · (C + D).

Building a POS expression from gates happens in two stages: OR gates first form each individual sum term such as (A + B), and then a single AND gate combines those sum terms together to produce the final output. Because the expression's overall structure is a product of the sum terms, the gate performing this final combining step is the one that represents a Product of Sum expression.

• OR gate builds only the inner sum term (the ‘+’ inside each bracket, e.g. A + B) — it never performs the outer combining of multiple sum terms, so naming it alone does not represent the full POS expression.

• EX-OR gate performs an exclusivity/parity check between its inputs, an operation that plays no part in constructing either a sum term or the outer structure of a POS expression.

• NOR gate is the complement of OR (true only when all inputs are false) — an inversion, not a combining operation, so it also plays no part in POS construction.

Hence, the AND gate is the gate that represents a Product of Sum expression.