what is the difference between Optical zoom and Digital zoom of a camera in a mobile phone?

Answer 1

Optical zoom is real zoom - the lens adjusts and you get a clear picture.

Digital zoom is done within the camera, and it just takes the image you have and resizes it, making it blurry.

Answer 2

Optical zooming is accomplished by moving the lenses.

Digital zoom stretches the image striking the the central portion of the image sensor to make it fit the entire sensor by multiplying the number of pixels displaying each color. The end result is a larger image with a loss of detail.

The higher the digital zoom number, the lower the image resolution. It's a trade-off!