问题 选择题

关于金属钠的性质描述不正确的是(  )

A.很软可用刀切割

B.在空气中燃烧生成白色的过氧化钠

C.金属钠通常保存在煤油里

D.钠具有银白色金属光泽,密度比水小

答案

A.钠是银白色金属,质软,可以用小刀切割,故A正确;

B.在空气中燃烧生成淡黄色的过氧化钠,氧化钠是白色固体,故B错误;

C.钠的密度大于煤油且和煤油不反应,所以可以用煤油隔绝空气来保存钠,故C正确;

D.钠是银白色金属,密度小于水,所以钠会浮在水面上,故D正确;

故选B.

多项选择题
多项选择题

The government has finally grown sick of claims that GCSEs and A-levels are being dumbed down, it seems. In his speech to the Labour Party conference on September 26th, Ed Balls, the schools secretary, said he would create a new watchdog to oversee exams. The current regulator is to be broken in two, with one bit continuing to develop new syllabuses and qualifications and reporting to ministers. The other bit, independent of government and reporting directly to Parliament, is to guard against grade inflation.
Mr. Bails draws parallels with Gordon Brown’s first big step when he became chancellor in 1997. Relinquishing the Treasury’s power to set interest rates to an independent body is still, ten years later, regarded as his finest hour. Mr. Balls, as his chief economic adviser at the time, was one of the architects of that decision. Both men hope that the new exams watchdog will lead to similar plaudits.
Britain’s secondary-school exam results have every reason to be upwardly mobile. The government wants voters to believe their children are getting a good education, so it is keen on high grades. Schools respond by shopping around among exam boards for the easiest syllabuses and tests, and directing pupils towards the softest subjects. Exam boards navigate between losing the trust of universities and losing the patronage of schools. And the individuals setting and marking exams know that harshness may mean fewer candidates in future.
The new arrangements may ensure that, in schools at least, bad exams do not drive out good. But they will have no effect on universities, where grade inflation is also rife. Three-fifths of all students now get at least an upper second, and between 2002 and 2006 the proportion of first-class honours degrees crept up from 9.7% to 11%.
There are also signs that the value of English degrees is being eroded on the international market. On September 25th the Higher Education Policy Institute (HEPI), a think-tank, published the results of a survey of 15,000 English undergraduates. It turns out that they spend much less time studying than those elsewhere in Europe. The average English student puts in 26 hours a week: 14 taught hours and the rest on independent study, compared with 29 hours in Spain and 41 in Portugal. Nor is it that English students are skimping on their studies to run to paid jobs ; students in other countries work harder outside university, too.
HEPI’s director, Bahrain Bekhradnia, cautions against a simplistic interpretation. Hours taught do not equal hours spent learning, he says, pointing out that tailored tutorials for small groups are likely to transmit more knowledge than the lectures in enormous amphitheatres that are routine at some continental universities.
But neither can the results be brushed away, he says. Foreign students may go elsewhere if they think an English undergraduate degree is content-light and poor value for money. This would spell financial disaster for many cash-strapped English universities. In 2004-05, the last year for which figures are available, they received 1.7 billion in foreign students’ fees.

At first sight the results of the third National Student Survey, published on September 12th, make more cheerful reading. That found that four-fifths of all English students considered their university experience satisfactory. But Graham Gibbs of Oxford University puts a gloomy spin on even this. What these students may be satisfied with, he says, "is an education that makes comparatively low demands on them". That is perhaps understandable: most undergraduates are not known for their work ethic. But it is short-sighted, both for them and their universities. After all, a currency can only trade for so long on its reputation.