问题 选择题

钠与水反应的现象与钠的下列性质无关的是(    )

A.钠的熔点低

B.钠的密度小

C.钠的硬度小

D.钠有强的还原性

答案

答案:C

题目分析:钠的密度小,浮在水面上。钠的熔点低,钠可以熔化成小球。钠的金属性很强,和水反应剧烈,钠四处游动,所以和钠的硬度无关,答案选C。

点评:钠和水反应是金属钠最重要的化学性质,需要熟练掌握。不但记住实验现象,还要会解释产生现象的原因。该题属于基础性试题,难度不大。

选择题
阅读理解

阅读理解

     Even plants can run a fever, especially when they're under attack by insects or disease. But unlike

human, plants can have their temperature taken from 3,000 feet away-straight up. A decade ago,

adopting the infrared(红外线)scanning technology developed for military purposes and other satellites,

physicist Stephen  Paley came up with a quick way to take the temperature of crops to determine which

ones are under stress. The goal was to let farmers precisely target pesticide(杀虫剂)spraying rather than

rain poison on a whole field, which invariably includes plants that don't have pest problems.

     Even better, Paley's Remote Scanning Services Company could detect crop problems before they

became visible to the eye. Mounted on a plane flown at 3,000 feet at night, an infrared scanner measured

the heat emitted by crops. The data were transformed into a colourcoded map showing where plants

were running "fevers". Farmers could then spotspray, using 50 to 70 percent less pesticide than they

otherwise would.

      The bad news is that Paley's company closed down in 1984, after only three years. Farmers resisted

the new technology and longterm backers were hard to find. But with the renewed concern about

pesticides on produce, and refinements in infrared scanning, Paley hopes to get back into operation.

Agriculture experts have no doubt the technology works. "This technique can be used on 75 percent of

agricultural land in the United States, " says George Oerther of Texas A & M. Ray Jackson, who recently retired from the Department of Agriculture, thinks remote infrared crop scanning could be adopted by the end of the decade.   But only if Paley finds the financial backing which he failed to obtain 10 years ago.

1. Plants will send out an increased amount of heat when they are________.

A. facing an infrared scanner

B. sprayed with pesticides

C. in poor physical condition

D. exposed to excessive sun rays

2. In order to apply pesticide spraying precisely, we can use infrared scanning to________.

A. estimate the damage to the crops

B. draw a colourcoded map

C. measure the size of the affected area

D. locate the problem area

3. Farmers can save a considerable amount of pesticide by________.

A. resorting to spotspraying

B. transforming poisoned rain

C. consulting infrared scanning experts

D. detecting crop problems at an early stage

4. The application of infrared scanning technology to agriculture met with some difficulties-________.

A. its high cost

B. the lack of official support

C. the lack of financial support

D. its failure to help increase production