So in calcium chlorate, there is one calcium, 2 chlorines, and 6 oxygens. To find the percent of oxygen in the compound, find the weight of the oxygen and divide it by the total weight of the compound:
weight of oxygen (95.94g/mol) / weight of entire compound (206.98g/mol)
= 0.4635
Finally, to convert this to a percentage you multiply it by 100
0.4635 x 100 = 46.35% Oxygen by mass
