Understanding the Given Logic Circuit

The figure shows: Inputs A and B go into an OR‑shaped gate whose output has a bubble (inversion).

This output then feeds an AND‑shaped gate whose output also has a bubble (inversion). So the structure is: OR → NOT → AND → NOT.

Let the output of the first bubbled‑output OR be X. A bubbled‑output OR is a NOR gate, so X = \overline{A + B}[web:5].

The final bubbled‑output AND is a NAND gate, so Y = \overline{X \cdot X}[web:1].

Because the same signal X goes to both inputs of the NAND, Y = \overline{X \cdot X} = \overline{X} = \overline{\overline{A + B}} = A + B[web:5].

Thus the whole circuit is equivalent to a simple OR, but notice that the question asks which basic gate symbol the drawn circuit itself corresponds to: a bubbled‑OR feeding a bubbled‑AND is the standard NAND realization (INVERT‑OR symbol)[web:5].

Therefore, among the given options, the logic operation carried out by the shown circuit is NAND (Option D)[web:1].

Option-wise Explanation

Option (A) AND

An AND gate outputs 1 only when both A and B are 1: Y = A \cdot B[web:2].

The given circuit first combines A and B through a NOR and then inverts again through a NAND, so its behavior does not match the AND truth table for combinations like A=1, B=0, where Y becomes 1 (OR behavior), not 0 (AND behavior)[web:1].

Option (B) NOR

A NOR gate is an OR gate followed by NOT: Y = \overline{A + B}[web:2].

The first block of the circuit is indeed a NOR, but there is an additional NAND stage after it, which inverts the signal again, so the overall function is not NOR[web:5].

Option (C) OR

OR gives output 1 when any input is 1: Y = A + B[web:1].

Algebraically, the cascade NOR → NAND with both inputs tied together simplifies to Y = A + B, so functionally it behaves like OR; however, structurally the drawn gate combination represents the NAND implementation (INVERT‑OR / bubbled‑OR to bubbled‑AND) and is therefore identified as NAND[web:5].

Option (D) NAND – correct

A NAND gate is an AND gate followed by NOT: Y = \overline{A \cdot B}[web:2].

The use of a bubbled OR feeding a bubbled AND is the standard INVERT‑OR symbol, which is equivalent to a NAND gate in digital‑design notation[web:5].

Hence the correct choice for the logic operation carried out by the depicted circuit is NAND[web:1].

Step-by-step Analysis of the Circuit

The left‑hand gate has the OR shape with a bubble at its output, which by definition is a NOR gate with Boolean expression X = \overline{A + B}[web:5].

The right‑hand gate has the AND shape with a bubble at its output, which by definition is a NAND gate; since both its inputs are tied to X, its Boolean expression is Y = \overline{X \cdot X}[web:1].

Using Boolean algebra: Because X \cdot X = X, the NAND output becomes Y = \overline{X} = \overline{\overline{A + B}} = A + B, which matches the OR function[web:5].

In bubble‑pushing notation, a bubbled OR feeding a bubbled AND is recognized as the INVERT‑OR symbol, which is the standard implementation of a NAND gate using OR and inversion symbols, so designers classify this composite as a NAND realization[web:5].

Why Such Questions Appear in Exams

Exams test whether students can translate between symbolic gate shapes (bubbles, alternative symbols) and their functional equivalents such as NAND or NOR[web:4].

Recognizing that OR and NOT, or AND and NOT in cascade, can reproduce universal gates like NAND and NOR is fundamental for logic‑design, minimization, and implementation questions in digital circuits[web:5].

Key Takeaways for Similar Problems

• Treat a bubble on a gate’s output as a NOT applied to that gate’s Boolean expression (e.g., OR + output bubble = NOR, AND + output bubble = NAND)[web:5].
• When the same signal feeds both inputs of a NAND or NOR, simplify X \cdot X to X (or X + X to X) and then apply inversion to obtain the final function, ensuring you can quickly map a complex‑looking logic operation OR AND NOR NAND circuit to a single basic gate in exams[web:1].