The answer is the lake.
A lake is a large expanse of terrestrial water, consisting of streams that are linked to the lake. Although some dimensions of some salt-water lakes are considered island seas; they are therefore distinct from the lagoons, and are larger and deeper than the ponds, while remaining a water body by definition.
If they are in the same row they have the same number of outer electrons on the same main shell also known as valence electrons
if they are in the same column they have the same number of valence electrons but on different main shells
Answer: Ionic formula will be 
.
Explanation: 
and 
ions will form a ionic compound. Ionic compounds have both metals and non-metals.
Here is a metal and is a non-metal.
The net charge on any compound must be 0.
So we need 2 phosphate ions to balance the charge on ions. Similarly we need 3 Magnesium ions to balance the charge on ions.
Criss-crossing the charges, we will get the formula as
Criss-crossing is shown in the image below.
