To find the gate equivalent to the given logic circuit, we need to determine the Boolean expression for the output
Y in terms of the inputs
A and
B.Step 1: Analyze Individual GatesThe circuit consists of three logic gates. Let's find the output of each:Top Gate (NOR): Takes inputs
A and
B.Output 1 =
A+B Bottom Gate (NAND): Takes inputs
B and
A.Output 2 =
A⋅B Final Gate (AND): Takes Output 1 and Output 2 as its inputs.
Y=(Output 1)⋅(Output 2)Y=(A+B)⋅(A⋅B) Step 2: Simplify the Boolean ExpressionWe can simplify
Y using De Morgan's Laws (
X+Y=Xˉ⋅Yˉ and
X⋅Y=Xˉ+Yˉ):From the first part:
A+B=Aˉ⋅Bˉ From the second part:
A⋅B=Aˉ+Bˉ Substitute these back into the equation for
Y:
Y=(Aˉ⋅Bˉ)⋅(Aˉ+Bˉ)Distribute
(Aˉ⋅Bˉ) over the terms in the parentheses:
Y=(Aˉ⋅Bˉ⋅Aˉ)+(Aˉ⋅Bˉ⋅Bˉ)Using the Idempotent Law (
X⋅X=X):
Aˉ⋅Aˉ=AˉBˉ⋅Bˉ=Bˉ The expression becomes:
Y=(Aˉ⋅Bˉ)+(Aˉ⋅Bˉ)Y=Aˉ⋅BˉApplying De Morgan’s Law in reverse (
Aˉ⋅Bˉ=A+B):
Y=A+BStep 3: ConclusionThe final expression
Y=A+B is the standard Boolean expression for a NOR gate.Verification via Truth Table

The output column for
Y matches exactly with a NOR gate.Correct Option: (4) NOR