How many molecules does 1.25 grams of C2H4 represent?

In a laboratory, 1.55mg of an organic compound containing carbon, hydrogen, and oxygen is burned for analysis. this combustion resulted in the formation of 1.45mg of carbon dioxide and .89 mg of water. what is the empirical formula for this compound?

Complete each row of the table below by filling in the missing prefix or missing exponent.

What is the molecular weight of copper