oxides/fluorides of a fictitious compund

If a fictitious compound - call it X
formed oxides X2O3 also X2O5,fluorides XF3 and XF5.
How do you determine the hydride and iodide formulas?
Thank`s for any help.

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The examples of an element X in your compounds are elements of a nitrogen group (N, P, As, Sb, Pb). Hydrogen valence is always I, and iodine valence is always I in the iodides. So it would be

XH3
XI3 (many of elements from N-group have many iodides; check this site)

NH3 NI3
PH3 PI3 ...

thank`s.
how can the same element form two different oxides such as X2O3 and X2O5?
how can I tell if compound X2O5 is stable or not?

"how can the same element form two different oxides such as X2O3 and X2O5?"

Well. most elements can do this.... they exhibit "more than one valency" .... or to phrase it another way, they can "exist in more than one oxidation state".

Basically, it depends on the reaction conditions.

The more agressive the conditions (eg, a very powerful oxidizing agent), the more more the element will be oxidized, to higher and higher oxidation levels.

(eg, the first row transition element manganese ....
I'm pretty sure if you look up its compounds, you'll see it in 7? 8? 9? different oxidation levels (some of them negative)
common oxides include MnO (oxidation level +2)
and MnO4- (permanganate ion ... oxidation level 7)

it's basically just down to how many electrons the element allowed the oxygen to steal off it in that particular reaction!

interesting reading,thanks.
so if an element forms oxides X2O3 and X2O5,fluorides XF3 and XF5.
from that info, can you deduce what element or what groups/periods it is in the periodic table?
Is it the 5th element down because of the "5"
would the oxide X2O5 and the fluoride X2F5 be stable compounds?
thank`s.

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