What are the rules for writing names/formulas for covalent
compounds? Give examples
where you need to produce
the formula from the name
AND the name from the
formula

When naming molecular compounds prefixes are used to dictate the number of a given element present in the compound. ” Mono-” indicates one, “Di-” indicates two, “Tri-” is three, “Tetra-” is four, “Penta-” is five, and “Hexa-” is six, “Hepta-” is seven, “Octo-” is eight, “Nona-” is nine, and “Deca-” is ten.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)