The ceiling fan capacitor is 2.25uf what will happen if we connect a capacitor of 2.5uf?

It is possible to use a ceiling fan capacitor with a higher uF, but it would change the speed of the fan.

As long as the capacitance is at least as large as the original, there should be no problem.

The fan is 120 volt, so there is no problem there.

Tolerances on these devices are routinely +/- 20% for high-quality caps.