B. There can't be good answers to stupid questions. For the polarity of NCl3 and SiI4, check Wikipedia. All compounds in question B react with water, so it's difficult to talk about solubility. NCl3 reacts relatively slowly, the other two very quickly. The solubility of Mg(OH)2 in water is a few mg per liter, so you won't get a 0.75 M solution under any circumstances.
G III. - when diluting the solution, the concentration decreases, but you did not throw away the moles of the substance in the trash.
H II. - simple stoichiometry 0.120 mol BaCl2 ==> 0.120 mol BaSO4 - just calculate the mass.
H III. You have a known amount of moles of chloride ions and you know the concentration and volume of iron (III) sulfate, so it's easy to calculate the molar concentration in the volume of 200 mL. You have precipitated virtually quantitatively barium and sulfate ions.
If significant numbers are important, check all responses for this.