(i) Substance B is anhydrous (fused) calcium chloride ().
(ii) Anhydrous calcium chloride absorbs the moisture present in the apparatus. This helps in keeping the anhydrous ferric chloride dry as it is a highly deliquescent salt.
(iii) Iron (III) chloride should be stored in a closed container because of its deliquescent nature. In the presence of moisture, iron (III) chloride absorbs water, gets dissolved in it and forms a saturated solution.
(iv) When dried chlorine gas is passed over heated iron, it forms anhydrous iron (III) chloride.
(b) The preparation of lead sulphate from lead carbonate involves the following steps:
Step I: Insoluble lead carbonate first reacts with dilute nitric acid to form soluble lead nitrate.
Step II: Dilute sulphuric acid is then added to lead nitrate to form lead sulphate and nitric acid.