How much are these onion magnified?

Answer 1

It depends on the strength of the lense you are using and how high you set the magnification of the microscope.
At 40X magnification, the microscope enlarges a 2 mm part of the onion and at 100X the microscope enlarges 0.8 mm of the cell. At both 40X and 100X you can online see a zoomed out image of the cells.

At 400X, the microscope enlarges a 0.2 mm part of the cell. The individual cell is more clearly seen.
At 1000X magnification, the microscope enlarges a 0.08 mm part of the onion cell. At this level of magnification the nucleus of the onion cell can be seen.

This link shows different magnifications of the onion cells.