What is the mass % of sodium chloride?

Question

An intravenous solution is analyzed to confirm its concentration. A 250 mL sample with a mass of 251.60 g is evaporated to dryness. The solid sodium carbonate residue has a mass of 2.27 g.

Answer 1

mass % NaCl = mass NaCl/mass of solution (x100%)

Your question asks for the mass % of sodium chloride, but the problem says it is sodium carbonate.  It makes no difference in this particular case, but if moles were involved, it would matter.

Solid solute = 2.27 g

total mass = 251.60 g (solute + solvent)

mass % of solute (NaCl or Na2CO3) = 2.27 g/251.60 g (x100%) = 0.902% by mass (to 3 significant figures)