问题 选择题

NA为阿伏伽德罗常数的值.下列叙述正确的是

A.常温常压下,46g的NO2和N2O4混合气体含有的分子数为NA

B.1mol Fe粉与1mol水蒸气充分反应转移的电子数为2NA

C.标准状况下,1L乙醇完全燃烧产生分子的数目为

D.中含有电子数为

答案

答案:B

题目分析:A、若气体全为NO2,分子数=46g÷46g/mol=1mol,若气体全为N2O4,分子数=46g÷92g/mol=0.5mol,所以46g的NO2和N2O4混合气体含有的分子数介于0.5NA ~ NA之间,错误;B、铁粉与水蒸气反应生成四氧化三铁和氢气,3Fe+4H2O Fe3O4+4H2,水蒸气完全反应,根据化合价的变化,转移的电子数为2NA,正确;C、标准状况下,乙醇为液体,不能用22.4L/mol计算物质的量,错误;D、1个CH3+含有8个电子,所以1mol CH3+中含有电子数为8NA,错误。

阅读理解

阅读理解。

     Five years ago, David Smith wore an expensive suit to work every day. "I was a clothes addict (有瘾的

人)" he jokes."I used to carry a fresh suit to work with me so I could change if my clothes got wrinkled (皱的)." Today David wears casual clothes-khaki pants and a sports shirt-to the office. He hardly ever wears a

necktie. "I am working harder than ever," David says, "and I need to feel comfortable." More and more

companies are allowing their office workers to wear casual clothes. In the United States, the change from

formal to casual office wear has been gradual. In the early 1990s, many companies allowed their employees

to wear casual clothes on Friday (but only on Friday). This became known as "dress-down Friday" or "casual

Friday"."What started out as an extra one-day-a-week benefit for employees has really become an everyday

thing," said a business consultant (顾问) Maisly Jones.

     Why have so many companies started allowing their employees to wear casual clothes? One reason is

that it's easier for a company to attract new employees if it has a casual dress code.""A lot of young people

don't want to dress up for work," says the owner of a software company, "so it's hard to hire people if you

have a conservative (保守的) dress code." Another reason is that people seem happier and more productive

when they are wearing comfortable clothes. In a study conducted by Levi Strauss Company, 85 percent of

employers believe that casual dress has a negative influence on morale (士气). Only 4 percent of employers

hold the opinion that casual dress has a negative influence on productivity. Supporters of casual office wear

also argue that a casual dress code helps them save money. "Suits are expensive, if you have to wear one

every day," one person said. "For the same amount of money, you can buy a lot more casual clothes."

1. David Smith refers to himself as having been"a clothes addict," in the first paragraph because ________.

A. he often wore khaki pants and a sports shirt

B. he couldn't stand a clean appearance

C. he wanted his clothes to look neat all the time

D. he didn't want to spend much money on clothes

2. David Smith wears casual clothes now, because ________.

A. they make him feel at ease when working

B. he cannot afford to buy expensive clothes

C. he looks handsome in casual clothes

D. he no longer works for any company

3. According to this passage, which of the following statements is FALSE?

A. Many employees don't like a conservative dress code.

B. Comfortable clothes make employees more productive.

C. A casual clothes code is welcomed by young employees.

D. All the employers in the U.S. support casual office wear.

4. According to this passage, which of the following statements is TRUE?

A. Company workers started to dress down about twenty years ago.

B. Dress-down has become an everyday phenomenon (现象) since the early 1990s.

C. "Dress-down Friday" was first given as a favor from employers.

D. Many workers want to wear casual clothes to attract people.

5. In this passage, the following strong points of casual office wear are mentioned EXCEPT ________.

A. saving employees' money

B. making employees more attractive

C. improving employees' motivation (动机)

D. making employees happier

名词解释