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Based on the principle of nomenclature, can we call H2S hydrogen sulfide instead of hydrosulfic acid?
This one's a little tricky.
The first important thing to realize here is that hydrogen sulfide, dihydrogen sulfide, dihydrogen monosulfide are all correct names for that compounmd, ##"H"_2"S"##, when it's in its standard state, i.e. when it's a gas.
Normally, you would use the Greek prefix di- when naming ##"H"_2"S"##, but you could skip it altogether.
The Systematic IUPAC name used for ##"H"_2"S"## is hydrogen sulfide.
The reason behind that is that hydrogen can only form a single covalent bond, and sulfur can usually form two covalent bonds.
This means that when sulfur bonds with hydrogen, you will automatically have two hydrogen atoms, so the Greek prefix di-, which you could still use if you wanted to, is omitted.
Now, when hydrogen sulfide is dissolved in aqueous solution, it becomes hydrosulfuric acid.
This is based on the fact that when you name an acid that's based on an element, the name of the acid must contain that element's full name.
Since sulfur is the element, the name of the acid must be hydrosulfuric acid, since hydrosulfic does not contain the full name of the element sulfur.
The name hydrosulfuic acid is thus given to the solution that contains dissolved hydrogen sulfide.
SImilarly, hydrogen chloride, ##"HCl"##, is the name given to the gas, and hydrochloric acid is the name given to the solution that contains dissolved ##"HCl"## molecules.