已知浓硝酸是一种易挥发的强酸，见光易分解，其分解的反应方程式为：4HNO₃$\stackrel{△}{=}$2H₂O+4NO₂↑+X↑．根据上述信息，回答下列问题：

（1）浓硝酸的化学性质：____ （写出一种即可）；

（2）水中氢、氧元素的质量比：____ （最简整数比）；

（3）判断X的化学式：____ ，判断依据是____ ；

（4）二氧化氮分子由氮原子和氧原子构成，其中氮原子的原子结构示意图为，氮原子的最外层上的电子数为____ ．

阅读短文，完成下列任务。

       Both the British and Americans speak English. However, there are several differences between American English and British English. For example, the words they use in daily life are not the same. The British call the first floor of a building the ground floor. The floor above the ground floor is the first floor, which Americans call the second floor. Once you go to Britain and America, you may notice other differences. The British usually hide their feelings. They don't often start a talk with strangers. On the train the British often spend their time reading newspapers or books. But Americans are more active and easier to talk with.