Option B is correct because the textbook explicitly states that 'Phosphorus salts are precipitated by liming.' Lime reacts with phosphorus inorganic compounds in the effluent to form insoluble calcium phosphate (Ca₃(PO₄)₂), which settles at the bottom of the settling tank and is removed. The other options are incorrect because: Organic compounds are removed using activated carbon filters (carbon absorption), not lime. Ammonia is removed by volatilisation through vigorous aeration at elevated temperature and high pH. Urea is not mentioned as being removed by lime in the provided context.