下列说法不正确的是（ ）
A．NCl3、PCl3、CO2、CCl4分子中各原子均达到8e－稳定结构
B．若R2－和M＋的电子层结构相同，则原子序数：R＞M
C．F2、Cl2、Br2、I2熔点随相对分子质量增大而升高
D．原子序数为34号的元素属于长周期的主族元素
答案：B
只要分子中元素化合价的绝对值和元素原子的最外层电子数之和满足8，则该原子就能达到8电子稳定结构，所以选项A中各原子均达到8e－稳定结构，A正确。若R2－和M＋的电子层结构相同，则原子序数是R小于M，B不正确。卤素单质的熔点随原子序数的增大而增大，C正确。原子序数为34号的元素Se，位于周期表的第四周期第ⅥA，属于长周期主族元素，D正确，答案选B。
Our sun is a star, and nine worlds move round it. Worlds like these are planets (行星). But there are other stars, other suns. Not only thousands of them, but millions of them. Do different stars have planets? We can see the planets round our own sun. But we haven’t seen any more. The stars are too far away from us. Stars give out (发出)light, but the planets don’t have any light of their own. So we can’t see them. They’re too far, and too dark. Still, we can tell that some stars have planets. While a big planet goes round, it pulls its star to one side. And sometimes we can see this, Then we know that the star has a planet. For example, Barnard’s Star（巴纳德星）is a small red star. And it is the quickest star in the universe. But sometimes it moves slower, and then quicker again. We have know Barnard’s Star for many years, and now we are sure it has a planet. 小题1:A star is a large body in the universe.it________.
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