Question

How many outer-shell d electrons are there in each of the following transition-metal ions?
Re(III)
Sc(III)
Ru(IV)
Hg(II)

Answer 1

Here is a link. Click on the element you want, scroll down the left side of the page and click on electron properties. You will find the electron configurations there. For example, click on Sc. You will see it has a 3d1 4s2. If it's the 3+ ion, it will have lost the 2 4s and the 1 3d electrons and will have zero in the 3d orbital.
http://www.webelements.com/

Answer 2

Not sure if you'll ever see this, Bob, but I really like how you force students to learn instead of just outright giving them the answers. Every single one of your posts have been really helpful. thank you very much!