Estimation Of Halogen (carius Method)

The Carius method estimates halogen by heating the compound with fuming nitric acid and silver nitrate, so that all halogen is precipitated quantitatively as the silver halide. Here the chlorine appears as silver chloride of molar mass 143.5 g mol^{-1}, which contains 35.5 g of chlorine per mole. The mass of chlorine in the precipitate = (35.5 / 143.5) × 0.287 = 0.071 g. Percentage of chlorine = (0.071 / 0.20) × 100 = 35.5%. Option 24.7% is the mass fraction of chlorine within AgCl itself and ignores the sample mass. Option 71.0% would arise from doubling the chlorine mass, equivalent to using half the true sample mass. Option 17.75% comes from mistakenly using twice the AgCl molar mass. The relation used is the NCERT Carius formula %X = (atomic mass of X × mass AgX)/(molar mass AgX × mass of compound) × 100. The reliability of the method rests on the halogen being precipitated completely and the silver halide being filtered, washed, and weighed without loss, so that the weighed mass faithfully represents all the halogen originally present. Plausibility check: chlorine content cannot exceed 100% and a value of 35.5% is reasonable for a moderately chlorinated organic molecule, so the answer is dimensionally and physically sound.