# Sort the following chromium compounds by whether the cation is chromium(II) or chromium(III)?

CrO

Chromium(II) compounds: CrO, Cr3P2, CrBr2
Chromium(III) compounds: CrN, Cr2P3, CrI3

NB. I’m assuming the CrL3 is a typo (there’s no element with that symbol), and you meant to have either CrCl3 or CrI3; either way, it’s a chromium(III) compound.

Chromium 2

The subscript gives the oxidation state of the Chromium ion. Anything with a subscript of 3 is Cr(III). The other two require a knowledge of valence. Oxygen has a valence of 2, so the Chromium is Cr(II). Nitrogen is 3.

Source(s): I’m a chemist!

O is almost always 2-, so Cr would be 2+ ==> Cr(II)
N is almost always 3-, so Cr would be 3+ ==> Cr(III)
P is usually 3-, so Cr would be 2+ (balance net charge: 2(-3) + 3(+2)=0 ==>. Cr(II)
Sulfur is usually 2-. so Cr would be 3+ (balance net charge: 3(-2) + 2(+3) = 0 ==> Cr(III)
I assume you meant I (iodine, not L which doesn’t exist): I = 1-, balance net charges ==> Cr(III)
Br is 1-, so again balancing net charge: 2(-1) + 1(+2) = 0 ==> Cr(II)

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chromium (II) : CrO , Cr3P2, CrBr2

chromium (III) : CrN, Cr2S3, CrL3