mono-	1
di-	2
tri-	3
tetra-	4

[[$\text{HCl}$]]	hydrogen chloride
[[$\text{H}_2\text{O}$]]	dihydrogen monoxide
[[$\text{CO}$]]	carbon monoxide
[[$\text{CO}_2$]]	carbon dioxide
[[$\text{H}_2\text{SO}_4$]]	dihydrogen sulphate, or sulfuric acid