Correct option: (1) One NAND gate
Explanation:
Gate I and II are used as NAND gates.Let their output be C1 and C2 respectively. C1 and C2 are inputs of gate III used as a NAND gate. Its output is C3 . C3 is input of gate IV used as a NOT gate. The final output C. The truth–table of the arrangement is
From the truth–table we can make truth–table showing A, B and C only. This is truth–table of a NAND gate. The arrangement therefore is equivalent to a single NAND gate.