Answer:
Because it is too dense for that to happen
Explanation:
Correct answer: 3. 
The given chemical reaction is between ammonium fluoride and magnesium chloride to form magnesium fluoride and ammonium chloride.
The balanced chemical equation representing the reaction will be,

The complete ionic equation for the reaction: All the compounds soluble in water (aqueous) will split into ions,
will not split into ions as it is insoluble in water.

The net ionic equation will be:

Here the spectator ions are 
Hi! I think the answer is option B. I hope
this helps, Goodluck :)
Exothermic is when energy is released
endothermic is when its being absorbed<span />
A because I said so I know so