What is the function of crystal in IC?

Answer 1

Not sure what your question means.

In an IC (Integrated Circuit) the circuit is etched onto a single crystal of Silicon. So the crystal forms the semiconductors within the IC.

or

Quartz Crystals are used in electronics as stable oscillators. They vibrate at precise frequencies, which can then be used for radio transmission or reception, or can form a time base for clocks or clock pulses, used for digital electronics.