List of top Science Questions on Writing Chemical Formulae

Write the chemical formulae of the following.
(a)Magnesium chloride
(b)Calcium oxide
(c)Copper nitrate
(d)Aluminium chloride
(e)Calcium carbonate

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.