http://www.webelements.com/tin/atoms.html
Look for the outer electrons.
A tin atom has 50 electrons. Electrons in which sublevel of this atom would experience the lowest effective nuclear charge?
a. 1s
b. 3p
c. 3d
d. 4s
3. 5p
3 answers
Oh, ok. So 5p?
right. Why? Because the 4p electrons have the shielding effect of the other 48 electrons in the lower levels so the attraction between the nucleus and the outer electrons are minimized.