A lot of people like sports. And some love 1 very much. An elephant can also 2basketball. There is an elephant. Its 3is Toktak. He 4 strong and cute. Many people like 5. Do you know 6? Because 7his free time, Toktak often plays basketball with his long trunk（象鼻）. He 8the sport very much. The basketball looks like a toy to Toktak. It is 9to watch Toktak playing basketball. Do you like the elephant? Let's 10him in the zoo. I think you can have fun there.

下列关于金属元素特征的叙述，正确的是（　　）

①金属元素的原子只有还原性，离子只有氧化性

②金属元素在化合物中一般显正价

③金属性越强的元素相应的离子氧化性越弱

④金属元素的原子最外层电子数都少于4．

点燃20克含有O₂、H₂、N₂的混合气体，充分反应后生成18克水，则剩余气体不可能是（　　）