Question 40 Which of the below given statement(s) is/are false about NAND Gate?
Qualcomm technical mcq question, verified with a worked answer. Free to practise - no sign-up.
Which of the below given statement(s) is/are false about NAND Gate?
I) NAND gate is combination of AND gate and NOT gate
II) NAND gate is the inverse of basic AND gate
III) The output of the NAND gate is equal to the complement of the output of the AND gate
IV) We can't design any basic logic gate by using NAND gate
Show answer & explanation
Statements I, II, and III are all true and describe the same concept from different angles: NAND is AND followed by NOT, making its output the complement of AND. Statement IV is false because NAND is a universal gate—you can design AND, OR, NOT, NOR, and XOR gates using only NAND gates.
Step-by-step Derivation:
Let's evaluate each statement:
I) NAND gate is combination of AND gate and NOT gate
✓ TRUE. NAND = AND + NOT. If A and B are inputs to AND, the output goes through a NOT gate.
II) NAND gate is the inverse of basic AND gate
✓ TRUE. Inverse means opposite/complement. NAND produces the complement of what AND produces.
III) The output of the NAND gate is equal to the complement of the output of the AND gate
✓ TRUE. This is the exact definition of NAND:
- AND: A·B
- NAND: (A·B)' = NOT(A AND B)
Truth table confirms: When AND outputs 1, NAND outputs 0, and vice versa.
IV) We can't design any basic logic gate by using NAND gate
✗ FALSE. NAND is a universal gate. You can construct:
- NOT: Connect both inputs together: (A·A)' = A'
- AND: Two NAND gates (first produces complement, second produces complement of complement)
- OR: Using De Morgan's Law: A + B = (A'·B')'
- NOR and XOR can also be designed
Therefore, only statement (IV) is false.