plz explain why is this the answer?

Question

why is the answer E, plz explain

What is the total number of electrons that can be accommodated in the level corresponding to n = 5?
A.
2
B.
8
C.
18
D.
32
E.
50


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and y is the answer E, plz explain

The hybridization of the central atom in KrF4O is:
A.
sp
B.
sp2
C.
sp3
D.
dsp3
E.
d2sp3

Answer 1

1) You really should study quantum numbers.
For n = 5, l = 0,1,2,3,4 and m = 0 for l=0, m=-1,0,1 for l=1, m=-2,-1,-,1,2 for l = 2, and so on. Hence there are 1+3+5+7+9=25 orbitals. For each orbital, ms = -1/2, 1/2, thus a total 50 electrons.
http://en.wikipedia.org/wiki/Quantum_numbers

2) Answer is again E: d2sp3.
Kr (n=4) has filled s and p orbitals. To make bonds with fluorine, it must kick 2 electrons to the nearby (available) d orbitals. It also accept 4 electrons from bonding fluorine atoms, thus making d2sp3 hybridization. It donate a pair of electrons to bond with oxygen, so all F and O atoms satisfy the octet rule.