Q.Mention any non-linear application of op-amp.

An operational amplifier (op-amp) is a compact integrated circuit that behaves as a direct-coupled, very high-gain differential amplifier. Its name comes from its early use in analog computers, where it carried out mathematical operations such as addition, subtraction, integration and differentiation.

Internally an op-amp is a chain of stages: a differential input stage that responds to the difference of its two inputs, a high-gain intermediate stage, a level-shifting (DC) stage and a low-impedance output stage. Externally it presents just a few terminals — an inverting input $(-)$, a non-inverting input $(+)$, the output, and dual supply pins $+V_{CC}$ and $-V_{EE}$. Its schematic symbol is a triangle pointing toward the output, with the two inputs on the left face. …