Question

Consider an atom of Xenon. How many electrons in this atom...
a) have the quantum number of l=2
b) have the quantum number of ml=0
c)have the quantum numbers n=5,ml=2 (at the same time)

I think I know the answers.
a) 10
b)2
c)2

But I am unsure and would like some input on if these are the right answers or not.

Answer 1

I believe you should rethink this carefully.

Answer 2

Now that I look closer at it, I think the answers may be
a)20 electrons
b)22 electrons

But I'm still unsure about c.

Answer 3

I agree now with both a and b .
c. The configuration is
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6.
So you have two with n = 5. s electrons have l = 0 and p electrons have l = 1 and d electrons have l = 2.
When l = 2, we may have m_l = -2, -1, 0, +1, and +2. So the only time m_l can be 2 is when we have a d electron and since there are no 5d electrons, we have no electrons with n = 5, m_l = 2 unless I've miscounted.

Answer 4

That makes sense. I wasn't thinking about the fact that the number in front of d is one less than n. Thank you.