Answer:
Option d, 1s2 2s2 2p6 3s2 3p6 4s2
Explanation:
Alkaline earth metals belong to group 2 of the periodic table. Elements belonging to group 2 are beryllium, magnesium, calcium, strontium and barium and radium.
Alkaline earth metals have 2 valence electrons and these two electrons are filled in outermost s sub shell.
General electronic configuration of alkaline earth metal: ns^2
In ionized state, number of electrons in s sub shell will not be 2.
Among the given, only 1s2 2s2 2p6 3s2 3p6 4s2, has 2 electrons in s sub shell. So, it an electronic configuration of neutral alkaline earth metal.
