Hello BobbJo, thank you once again for the instant replies.
However, in the question, I believe that somehow the key word is stable/unstable. Why the same word meant that the starters of the 3 bullet points are at a higher energy?
In the first bullet point, MgCl is stable with respect to magnesium and chlorine : I assume this means that the attractive forces between the oppositely charged ions hold the structure firm ( giant ionic lattice ). However, does being stable mean that it releases energy? I don't think so however I am willing to listen always but I do have this opinion because I would believe it would release energy if it is standard enthalpy of atomisation as gases are formed just like combustion releases energy but the question states the compounds in solid states. Kindly explain this.
In the second bullet point, although MgCl is unstable, you have still stated that it releases energy despite the question mentioning that MgCl is unstable - why a different word was given the same attribute?
In the 3rd bullet point, why the same word ( unstable ) was given a different attribute compared to the 2nd bullet point ( and 1st bullet point ) This time you said it's endothermic.
Thank you once again BobbJo, would always love to have your explanations.