Molar concentration is the amount of solute in moles divided by 1 liter of solvent. Then to answer this question, you need to convert the 23g of ammonium chloride into mole unit. Since the mass of nitrogen = 14, helium =1, and chlor= 35.453 then the molecular mass of (NH4)Cl should be: 14+4+35.453= 53.5
Then, the molarity should be: 23g/ (53.5gr/mole)/ (500ml/1000ml)= 0.86molality