Consider the two electron arrangements for neutral atoms a and b. what is the atomic number of b? a - 1s2, 2s2, 2p6, 3s1 b - 1s2, 2s2, 2p6, 5s1

The order of the orbitals is shown in the picture attached. This ordered arrangement is a guide to know the electronic configuration of a certain element. You can't skip an orbital, that's why 5s after 2p orbital is not possible. For element b, count the exponents of each orbital because they represent the electrons.

# of electrons = 2+2+6+1 = 11

Element 11 in the periodic table is Sodium (Na).

7is b8 is d9 is c10 is a11 is d