Answer:
c. NH₄C is soluble in water because NH₄ always creates soluble solutions. This is because of it's high electronegativity of 5.4, which makes any compound with NH₄ ionic, and therefore soluble in water.
Explanation:
Look at the Solubility Guidelines to find which compound is soluble in water.
a) It says that hydroxide (OH⁻) creates insoluble compounds, and copper does not change this. Cu(OH⁻) is not soluble in water,
b) Carbonate (CO₃²⁻) also creates insoluble compounds, so B is also incorrect.
c) Ammonium (NH₄) creates soluble compounds with no exceptions, so C must be the correct answer.
We can make sure of this by checking if NH₄C is polar. This will prove that it is soluble in water because water is a polar molecule. We know that like dissolves like, meaning polar solvents will dissolve polar solutes, but not non-polar solutes. Polar solvents also dissolve ionic substances because, instead of dipoles of polar solutes being separated because of attraction to dipoles of the solvent, the cations and anions will separate based on attraction to dipoles the same way.
Hydrogen has an electronegativity of 2.2, but there are for H ions present in NH₄ so they have a total charge of 8.8. Nitrogen has an electronegativity of 3.0. The difference of 8.8 and 3.0 is 5.4. Carbon has an electronegativity of 2.6. We need the difference between the NH₄ and C, which is 2.8. Ionic solutions must have an electronegativity greater than 1.7. 2.8>1.7, so NH4C is an ionic compound, and it is soluble in water.