These are two questions and two answers.
Question 1: Which best defines concentration?
Answer: option A, ratio that describes the amount of solute divided by the amount of solvent or solution
Explanation:
There are many different measures of concentration: percent, molarity, molality, mole fraction are some examples.
All of them express the ratio of solute to solvent or solution, in different kind of units, may be mass, number of moles, or volume.
Molarity is number of moles of solute per liter of solution. Molality is number of moles of solute per kg of solvent.
So, as you see it is always a ratio of the amound of solute, but it is not a fixed unit.
Question 2. Which contributes to the dissolution of sugar in water?
Answer: option D, a strong pull of water molecules on a polar covalent compound.
Explanation:
Sugar is not a ionic compound so it does not dissociate.
Sugar is a molecule, so it remains as such in solution.
Sugar is polar, so it can be dissolved in water that is a polar solvent (like dissolve like, is the rule).
The dissolution is explained by the fact that the pull exerted by the molecultes of solvent on the molecules of solute, is greater than the pull that the molecules of solute extert among themselves.
That permits the molecules of solvent surround the molecules of solute and get them appart of the solid substance to form the aqueous solution.
