so for all the chemical formulas if there is no subscript (for the valency of the element) does it mean it is a one or do i have to find the valency on the periodic table of elements?

Question

ex. P02
the P for Phosphorus doesn't have a number does it mean it is a one then
ex.SO3
ex.FeCl3
ex.SnCl2
ex.Cu2O
ex.NiBr2
and can you check my answers for and can you tell me which ones are wrong and to correct it...
SnCl2 = Tin(II)Chloride

Cu2O = Copper(I)Oxide

NiBr2 = Nickel(II)Bromide

FeO = Iron(II) Oxide

SbBr5 = Antimony(V)Bromide

CoO = Cobalt(II)Oxide

MnF2 = Manganese(II)Fluoride

SnO2 = Tin(II)Oxide

SO2 = Tin(I)Oxide

BrF7 = Bromine(VI)Fluoride

1. Cobalt(II)Chloride = Co2Cl = CoCl2

2. Sulphur(II)Iodide = S2I1 = SI2

3. Iron(III)Chloride = Fe3Cl1= FeCl3

4. Antimony(V)Sulphide = Sb5S2 = Sb2S5

5. Lead(II)Nitride = Pb2N3 = Pb3N2

6. Tin(II)Fluoride = Sn2F1 = SnF2

7. Copper(II)Oxide = Cu2O2 = CuO

8. Tin(IV)Chloride = Sn4Cl1= SnCl4

9. Mercury(I)Phospide = Hg1P3 = Hg3P

i know that it is a lot of questions but i only put that many is because i am scared that i wont understand with only 1 or 2 examples if and when i am wrong so plz check and answer ASAP cause i need help for it

Answer 1

Yes, if no subscript is shown it is understood to be 1.
For the first part all are ok except these two.

SO2 = Tin(I)Oxide
S is sulfur (not tin) and I would name this sulfur dioxide but I believe the IUPAC name would be sulfur(IV) oxide.

BrF7 = Bromine(VI)Fluoride
Wouldn't this one be bromine(VII) fluoride? bromine (VI) fluoride would be BrF6.

For the last group I think you have a problem. The last formula you wrote in each line is correct for every one of the compounds listed; however, what you have in between is not right for any of them. For example, Co2Cl IS NOT = CoCl2. CoCl2 is the correct formula for cobalt(II) chloride. You may be using a mnemonic or some memory device to help you come up with the right answer and if it helps you (because all of them are right) ok; however, putting in that middle step on paper is not right. I suspect your prof would give you a failing grade. So do that middle step, if it helps you, in your head but don't write it down. I'm assuming this is a device to help you get it correct. It is isn't; i.e., if you have written both in the hopes one is correct let me know for we need to go through to get them right. Profs will not pick and choose the right answer in these instances.