How many outer-shell d electrons are there in each of the following transition-metal ions?
re(iii) =
sc(iii) =
ru(iv) =
hg(ii) =

The answer to your question is:

Re (III) has 5 electrons

Sc(III) =  has 1 electron

Ru(IV) =  has 6 electrons

Hg(II) = has 10 electrons

Explanation:

75 Re(III) =  1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d⁵

21 Sc(III) =   1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹

44 Ru(IV) =  1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁶

80 Hg(II) =  1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰