A is 1. Each letter corresponds to what place they are in the alphabet
O2 is an example of a molecule
1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 3d^5, 4s^1
Chromium is strange because it moves on to the 4s orbital instead of filling the 3d orbital with that last electron. Tricky.
Mark as brainliest if this helped! :)
I believe you would just put a 2 in front of NH3 and keep the other ones as 1
