What is the total number of valence electrons in a calcium atom in the ground state?
(1) 8 (3) 18
(2) 2 (4) 20

In its ground state Calcium has a 2 valence electrons.

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom