Answer
Be, Mg, and Ca have similar chemical properties.
Work Step by Step
a. Beryllium has 4 electrons.
Consider the subshells in the order of increasing energy.
An s subshell holds 2 electrons, p subshells hold 6 electrons, and d subshells hold 10 electrons.
This is the ground-state electron configuration for beryllium.
$$1s^2 2s^2$$
b. Magnesium is below Be in the periodic table, with Z=12.
$$1s^2 2s^2 2p^6 3s^2$$
c. Calcium is below Mg in the periodic table, with Z=20.
$$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$$
