Number of moles of ions produced by complete dissociation of one mole of Mohr's salt in water is 5.

Mohr's salt, also known as ferrous ammonium sulfate, has the chemical formula FeSO4(NH4)2SO4·6H2O. When it dissolves in water, it undergoes complete dissociation into its constituent ions. Let's break down the dissociation of Mohr's salt:

1. Ferrous ion (Fe2+):
Each mole of Mohr's salt produces one mole of Fe2+ ions. This is because there is one Fe2+ ion in the formula of Mohr's salt.

2. Sulfate ion (SO4^2-):
Each mole of Mohr's salt produces one mole of SO4^2- ions. This is because there is one SO4^2- ion in the formula of Mohr's salt.

3. Ammonium ion (NH4+):
Each mole of Mohr's salt produces two moles of NH4+ ions. This is because there are two NH4+ ions in the formula of Mohr's salt.

Therefore, the total number of moles of ions produced by complete dissociation of one mole of Mohr's salt can be calculated as follows:

1 mole Fe2+ + 1 mole SO4^2- + (2 moles NH4+) = 4 moles of ions

However, we need to consider the water of crystallization, which is represented by the formula 6H2O. This means that each mole of Mohr's salt contains six moles of water molecules. When Mohr's salt dissolves in water, these water molecules also dissociate into H+ and OH- ions. Since there are six water molecules per mole of Mohr's salt, we have:

6 moles H+ + 6 moles OH- = 12 moles of ions

Adding this to the previous calculation, we get:

4 moles of ions + 12 moles of ions = 16 moles of ions

However, we need to account for the fact that the H+ and OH- ions are already present in water and do not come from the dissociation of Mohr's salt. Therefore, we subtract 12 moles of ions from the total:

16 moles of ions - 12 moles of ions = 4 moles of ions

So, the correct answer is option C: 5 moles of ions.