Which of the following ionic compounds would have the most negative lattice energy: NaCl, KCl, or MgCl2? Explain your answer.

MgCl2

Explanation:

Lattice energy will be higher on ion with higher charge, or smaller size. A higher charge means it will have a stronger force. Smaller size ion will have less distance.  

Magnesium has +2 charge and located in the third row, make it strongest of these three. Natrium will be the second strongest even though its charge is +1, the same as Kalium. Natrium has smaller size as it is on the third row, compared to Kalium that was in the fourth row.

the electronic configuration of an atom with eight electrons is 1s²2s²2p⁴. the orbital diagrams are shown in the figure.

as per the hunds rule:

1. electrons tend to avoid being in the same orbital as per as practicable.

2. electrons in different orbitals of the same energy will have their spin parallel.

this can be illustrated from the multiplicity of the orbitals of the atom. as there are four electrons in the p orbital and p orbital has 3 sub-shells. the electrons can be fed in different ways as shown in the figure but the correct orbital diagram will be as per the hunds rule.

its first and third is your answer i did the qustion the fourth isnt right