Chemistry and balancing equations +subscripts of elements?

u need to look at your periodic table and find out whether the element is in which group.
For example calcium hydroxide,
calcium is in Group II, that means Ca will have 2 valence electron (+2 oxidation state). Ca superscript 2+ .
Then for hydroxide, the oxidation number is -1. OH superscript 1-.
Then when the two ions form bond both oxidation number cross over. So, it will be Ca(OH)subscript 2.

For balancing of equation, there is no unique for me work out. Just have to make sure that the no. of elemtens on the left is equal to the right.

Sodium Phosphate
1. Na =1positive charge + PO4 = 3 negative charge
2. you see 3 sociums are requred for every phosphate to cancell 3 negative charges against 3 positive charges.
3.Therefore 3Na+PO4...> ?
if we write 3NaPO4 then we have 3Ma + 3PO4 (3 positive charges and 9 negative charges and the formulae is incorrect)
4. so we write Na3PO4 .. here we have 3 Na and 1 PO4 or 3 positive charges and 3 negative charges.
 The program here does not permit me to show you an easy way out