What is the empirical formula of a substance that consists of 0.910 g calcium, 0.636 g nitrogen, and 1.453 g oxygen?

You need to change them to mole

mole = mass / Molar mass

mole of Ca = 0.910 g / 40.08 g/mol = 0.0227 mol

mole of N = 0.636 g / 14.01 g/mol = 0.04539 mol

mole of O = 1.453 g / 16.00 g/mol = 0.0908 mol

Then, take the smallest number and divide for all number (in mol that I just found)

Ca = 0.0227 / 0.0227 = 1

N = 0.04539 / 0.0227 = 1.9999 (round it 2)

O = 0.0908 / 0.0227 = 4

So the empirical formula will be Ca1N2O4 (CaN2O4)