Do you think that my Solutions are right?

Question

We had a quiz in chemistry and I was just wondering if my answers are right. The exercise was about "CORE ELECTRONIC CONFIGURATION", and these are my answers.:

Given/Solution:

1. [Na] Sodium = [Na] 2p6 3s1<--- Electronic Configuration

Last M: 3 and the Valence: 1

2. [I] Iodine = [I] 4d10 5d5

Last M: 5 and the Valence: 5

3. [Ar] Argon = [Ar] 3d4 4s2

Last M: 4 and the Valence: 2

-----> If my answers are wrong please explain. Thank you!

Answer 1

Sodium you need to find a home for 11 electrons:
the configuration is: 1s2, 2s2, 2p6, 3s1 (1 valence electron)

Argon is easy: 18 electrons:
1s2, 2s2, 2p6, 3s2, 3p6 (we have a filled octet, no valence electrons)

Iodine we have 55 electrons! Things get a bit complicated
1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2, 4p6, 4d10, 5s2, 5p5 there are 7 valance electrons.

When filling orbitals, fill the lowest vacant s-orbital first, then the p orbitals, Remember, at (K,Ca) the 4s orbital fills before the 3d starts filling, once the 3d is full, fill the 4p, then the 5s, then the 4d, then 5p etc. Unfortunately there are a few elements that don't obey the rules!