How many lone pairs of electrons are present in the lewis structure of calcium sulfide?

            Four

Explanation:
                     Calcium Sulfide is an ionic compound made up of Ca²⁺ and S²⁻.
Ca²⁺ is formed as,

                                   Ca    →    Ca²⁺  +  2 e⁻

These two electrons are accepte by Sulfur as,

                                     S  +  2 e⁻    →    S²⁻

So, before accepting 2 electrons S was having six valence electrons, after accepting two electrons from Ca it has 8 electrons which are present in four pairs as shown below,