No it's not hard and fast rule that u have to write answer in a same way which have been given in ncert books or any other book. If u know the answer then represent it in ur way. For chemistry chapter 5,6,9,8,7,14,15,16 mug up these all chapters as mostly questions come directly from them. Board checking is depend on examiner. Give ur best and keep the answer sheet neat and clean. Answer only point to point in chemistry specially. All the best.