All students need to have good study habits(习惯). When you have good study habits, you can learn things quickly. You also remember them easily. Do you like to study in the living-room? This is not a good place because it is usuallytoo noisy. You need to study in a quiet place, like your bedroom. A quiet place will help you only think about one thing, and you will learn better. Before you begin to study, do not forget to clean your desk. A good desk light is important, too. You are feeling tired easily if there is not enough(足够的) light.

方程组$\left\{\begin{array}{c}x+y=5\\ x-y=1\end{array}\right.$的解是（　　）

 84消毒液是一种有刺激性气味的高效液体消毒剂．主要成分为次氯酸钠（NaClO），广泛用于宾馆、旅游、医院、食品加工、家庭等的卫生消毒．请阅读信息并回答：

（1）次氯酸钠的制取原理是氯气与氢氧化钠反应生成氯化钠，次氯酸钠和水，化学反应方程式为　____ ；

（2）消毒液中次氯酸钠自身没有消毒作用，有消毒作用的是次氯酸钠与空气中二氧化碳反应得到的次氯酸（HClO），化学方程式为　____　；

（3）84消毒液是含氯消毒剂，氯气是一种挥发性的有毒气体，因此，84消毒液必须____保存．