问题 填空题

1H、D、T三种原子:

(1) 在同温同压下,它们的单质的密度之比是         

(2) 1mol各种单质中,它们的质子数之比是         

(3) 1g各种单质中它们的中子数之比是         

(4) 在标准状况下,1L各种单质中,它们的电子数之比是         

答案

(1)  1∶2∶3 ;(2)  1∶1∶1 ;(3)  0∶3∶4 ;(4)  1∶1∶1 。

题目分析:(1)质量数=质子数+中子数,三种原子的质量数分别为1、2、3,故在同温同压下,体积相等,故根据密度=质量/体积,故密度之比为1:2:3.

(2)三种原子的质子数都为1,故质子数为1∶1∶1。

(3)三种原子的中子数分别为0、1、2,而三种原子的质量数分别为1、2、3,故1g各种单质分别含有0、1/2、1/3个原子,故中子数分别有0、1/2、2/3,即中子数之比为0∶3∶4。

(4)在标准状况下,1L各种单质都含有22.4mol个原子,而三种原子所含的电子数相同,故电子数之比为1∶1∶1。

点评:此题考核了同位素的相关性质,要记住几个关系式和相关概念,质量数=质子数+中子数,及同种元素原子的原子核中,中子数不一定相等。

配伍题 B型题
单项选择题

Shopping has always been something of an impulse activity, in which objects that catch our fancy while strolling are immediately bought on a whim. Advertisers and sellers have taken advantage of this fact, carefully positioning inexpensive but attractive items on paths that we are most likely to cross, hoping that our human nature will lead to a greater profit for them. With the dawn of the Internet and its exploding use across the world, the same tactics apply.

Advertisers now place "banners", links to commercial web sites decorated with attractive pictures designed to catch our eyes while browsing the webs, on key web sites with heavy traffic. They pay top dollar for the right, thus creating profits for the hosting web site as well. These actions are performed in the hopes that during the course of our casual and leisurely web surfing, we’ll click on that banner that sparks our interest and thus, in theory, buy the products advertised.

Initial results have been positive. Web sites report a huge inflow of cash, both from the advertisers who tempt customers in with the banners and the hosting web sites, which are paid for allowing the banners to be put in place. As trust and confidence in Internet buying increases and information security is heightened with new technology, the volume of buying is increasing, leading to even greater profits.

The current situation, however, is not quite as optimistic. Just as magazine readers tend to unconsciously ignore advertisements in their favorite periodicals, web browsers are beginning to allow banners to slip their notice as well. Internet users respond to the flood of banners by viewing them as annoyances, a negative image that is hurting sales, since users are now less reluctant to click on those banners, preferring not to support the system that puts them in place. If Internet advertising is to continue to be a viable and profitable business practice, new methods will need to be considered to reinvigorate the industry.

With the recent depression in the technology sector and slowing economy, even new practices may not do the trick. As consumers are saving more and frequenting traditional real estate businesses over their Internet counterparts, the fate of Internet business is called into question. The coming years will be the only reliable indication of whether shopping on the world wide web is the wave of the future or simply an impulse activity whose whim has passed.

The author’s attitude toward online advertising can be summarized as()

A. reserved consent but discontent

B. objective analysis void of opinions

C. enthusiastic support but slight contempt

D. approval so far but uncertainty in the future