15.K is the chemical symbol of Potassium and generally the name of the non-metal at the end of a formula has the suffix '-ide' and since O is oxygen, the name becomes Potassiumoxide.
16. The same applies here. Ca is Calcium and Cl is Chlorine but since its the non-metal at the end, it ends in -ide. So Calcium chloride.
17.The same applies here too. Al is Aluminium and S is Sulphur so Aluminium sulphide.
18. Calcium's symbol is Ca and that of Sulphur is S and that gives the formula CaS.
1 is D - double-replacements do not make solid metals 2 is A - to have complete combustion the original compound must ONLY have C, H and O 3 is B - the elemental Mg replaces the H in the HCl
