Work this out like this Chroium you are told is oxidation state +3. Selenium is in group 16 along with oxygen and sulfur so it will have a preferred oxidation state of -2. Then balance it, oxidation staes can be treated like ionic charges:-
Cr2Se3
The chemical formula for chromium nitrate is Cr(NO3)3.
That would be chromium(II) sulfate, but really, chromium mostly exists as Cr(III) or Cr(VI), which would change the formula.
The chemical formula for chromium(III) oxide is Cr2O3. It is a dark green solid compound that is commonly used in the manufacturing of pigments, ceramics, and refractory materials.
The chemical name for the compound Cr2(SO3)3 is chromium(III) sulfite.
CrO is the formula for chromium(II) oxide. Cr is the elemental symbol for chrome, and O represents oxygen. The molecular weight of CrO is 68.00 grams/per mole using two significant figures. Variants of CrO include II, III and VI.
The chemical formula of iron(III) and selenium is Fe2Se3 - iron(III) selenide.
The chemical formula for chromium(III) iodide is CrI3.
The chemical formula for chromium (III) sulfate is Cr2(SO4)3.
The chemical formula of chromium(III) arsenate is CrAsO4.
The chemical formula for chromium phosphide is CrP.
the chemical formula for chromim(II) fluoride is CrF2
The chemical formula for chromium nitrate is Cr(NO3)3.
Chromium(III) borate has the chemical formula CrBO3.
The chemical formula for chromium III carbonate is Cr2(CO3)3. When it decomposes, it yields chromium III oxide (Cr2O3) and carbon dioxide (CO2).
Cr2O3 is the chemical formula for chromium (III) oxide
CrPO4 is the chemical formula for Chromium(III) phosphate, a compound composed of chromium (III) cations and phosphate anions. It is commonly used in the manufacturing of ceramics and as a catalyst in organic reactions.
Cr(SCN)3 is the chemical formula for the Chromium (III) Thiocyanate. This is because Chromium (III) has a charge of +3 while Thiocyanate has a charge of -1. To balance the charges, we switch the 2 charges. So we have 1 ion of chromium (III) with 3 ions of thiocyanate.