<u>Answer:</u> The balanced chemical equation is written below.
<u>Explanation:</u>
Double displacement reaction is defined as the reaction in which exchange of ions takes place.

Precipitation reaction is defined as the reaction in which an insoluble salt is formed when two solutions are mixed containing soluble substances. The insoluble salt settles down at the bottom of the reaction mixture.
When nickel (II) chloride reacts with silver (I) nitrate, it leads to the formation of white precipitate of silver chloride and an aqueous solution of nickel (II) nitrate.
The balanced chemical equation for the above reaction follows:

By Stoichiometry of the reaction:
1 mole of aqueous solution of nickel (II) chloride reacts with 2 moles of aqueous solution of silver (I) nitrate to produce 2 moles of solid silver chloride and 1 moles of aqueous solution of nickel (II) nitrate
Hence, the balanced chemical equation is written above.
Explanation:
Atomic number of magnesium is 12 and its electronic distribution is 2, 8, 2. On the other hand, atomic number of iodine is 53 and its electronic configuration is
.
Hence, there are 7 valence electrons in an iodine atom and there are 2 valence electrons in a magnesium atom.
So, one atom of iodine requires one electron from a donor atom to complete its octet. But one magnesium atom contains two valence electrons.
Therefore, one magnesium atom will combine with two iodine atoms to result in the formation of magnesium iodide as follows.

Therefore, an ionic bond will be formed when magnesium reacts with iodine to make magnesium iodide.
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