Introduction:
An operational amplifier (op-amp) is an integrated circuit that is widely used in electronic circuits. It has three main terminals: the inverting terminal, the non-inverting terminal, and the output terminal. These terminals play crucial roles in determining the behavior and functionality of the op-amp.

Inverting Terminal:
- The inverting terminal, also known as the negative input terminal, is denoted by a negative sign (-).
- When a voltage is applied to this terminal, the output voltage of the op-amp is inverted and amplified.
- The inverting terminal is typically used to create an inverting amplifier or a summing amplifier.

Non-inverting Terminal:
- The non-inverting terminal, also known as the positive input terminal, is denoted by a positive sign (+).
- When a voltage is applied to this terminal, the output voltage of the op-amp is non-inverted and amplified.
- The non-inverting terminal is typically used to create a non-inverting amplifier or a voltage follower.

Output Terminal:
- The output terminal is denoted by the symbol "O".
- It is the terminal from which the amplified signal is obtained.
- The output voltage of the op-amp is determined by the voltages present at the inverting and non-inverting terminals.

None of the mentioned:
- The statement "None of the mentioned" is incorrect.
- All three terminals mentioned above are essential and present in an operational amplifier.
- Each terminal serves a specific purpose in the amplification and signal processing functions of the op-amp.
- Therefore, the correct answer to the question is not "None of the mentioned."

Conclusion:
In summary, an operational amplifier has three main terminals: the inverting terminal, the non-inverting terminal, and the output terminal. Each terminal has a unique function in determining the behavior and functionality of the op-amp. Therefore, the correct answer is not "None of the mentioned."