问题 选择题

最近,大米中镉超标受到人们广泛关注。镉有剧毒,首先引起肾脏损害,然后破坏人体内的钙,使人患上无法忍受的骨痛病。结合图示判断,下列关于镉的说法错误的是( )

A.是一种对人体有害的金属元素

B.相对原子质量为ll2.4

C.原子序数和原子核内中子数均为48

D.原子核外有5个电子层,最外层有2个电子

答案

答案:C

题目分析:根据原子结构示意图和元素周期表的知识。图片中各类符号的意义如下图所示:

A、食用含镉的食物后,可引起肾脏损害,然后破坏人体内的钙,使人患上无法忍受的骨痛病,是一种对人体有害的金属元素,A正确;B、从图中可看出,镉相对原子质量为ll2.4,B正确;C、原子序数=核电荷数=核外电子数=质子数,镉原子的原子序数为48,中子数=相对原子质量-质子数=112-48=64,C错误;D、从图中可看出,镉原子核外有5个电子层,最外层有2个电子,D正确。故选C

单项选择题

(一) Friends play an important part in our lives, and although we may take the friendship for granted, we often don’t clearly understand how we make friends. While we get on well with a number of people, we are usually friends with only a very few, for example, the average among students is about 6 per person. In all the eases of friendly relationships, two people like one another and enjoy being together, but beyond that, the degree of intimacy between them and the reasons for their shared interest vary enormously. As we get to know people we take into account things like age, race, economic condition, social position, and intelligence. Although these factors are not of prime importance, it is more difficult to get on with people when there is a marked difference in age and background. Some friendly relationships can be kept on argument and discussion, but it is usual for close friends to have similar ideas and beliefs, to have attitudes and interests in common--they often talk about ’ being on the same wavelength’. It generally takes time to reach this point. And the more intimately involved people become, the more they rely on one another. People want to do friends favors and hate to break a promise. Equally, friends have to learn to put up with annoying habits and to tolerate differences of opinion. In contrast with marriage, there are no friendship ceremonies to strengthen the association between two people. But the supporting and understanding of each other that results from shared experiences and emotions does seem to create a powerful bond, which can overcome differences in background, and break down barriers of age, class or race.

According to the author,______

A.all those who get on well with each other are friends

B.friends are closer than people who just get on well with each other

C.everyone understands clearly how to make friends

D.every student has 6 friends

问答题