下列判断中一定正确的是
A．若R2-和M+的电子层结构相同，则原子序数：R>M
B．若X、Y都是气态氢化物，且相对分子质量：X>Y，则沸点：X>Y
C．若M、N是同主族元素，且原子序数：M>N，则非金属性：M>N
D．若X、Y属于同主族元素，且相对原子质量：X>Y，则X失电子能力比Y的强
答案：D
题目分析：A、若R2-和M+的电子层结构相同，则离子的核外电子数相同。由于前者是阴离子，质子数＝核外电子数－2，后者是阳离子，质子数＝核外电子数＋1，所以原子序数：R＜M，A不正确；B、一般情况下，氢化物的相对分子质量越大，沸点越高。但由于HF、H2O以及NH3分子中存在氢键，因此沸点高于同主族元素氢化物的沸点，B不正确；C、同主族自上而下，非金属性逐渐减弱，因此若M、N是同主族元素，且原子序数：M>N，则非金属性：M＜N，C不正确；D、同主族自上而下金属性逐渐增强，相对原子质量逐渐减小，所以若X、Y属于同主族元素，且相对原子质量：X>Y，则X失电子能力比Y的强，D正确，答案选D。
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| It seems that the cities in the future will have to change. Because the world's population __1__ , there will be __2__ people in the cities tomorrow. It may be __3__ for any family to live in a house with land around it. There__4__ enough space for them. __5__ to solve this problem may be the skyscraper city (摩天城). The highest building in the world  today is in Taipei. It's about 509 metres high. The skyscraper cities in the future will be many times __6__ . In a skyscraper city about 250,000 people will live. Nearly a million people can __7__ in four of these great buildings. Each skyscraper city will have four towns in it and each town will have ten villages. They will live, work and __8__ their free time in them. They won't need to leave the city __9__ they want to. They will be able to move about in the city by transport controlled __10__ computers. Let's imagine how the life will be then! | |||
| ( ) 1. A. has grown ( ) 2. A. many ( ) 3. A. impossible ( ) 4 A. aren't ( ) 5. A. A way ( ) 6. A. lower ( ) 7. A. live ( ) 8. A. spend ( ) 9. A. until ( ) 10. A. by | B. is growing B. much B. possible B. won't be B. A road B. shorter B. study B. cost B. when B. at | C. are growing C. more C. important C. won't have C. An answer C. taller C. work C. pay C. while C. with | D. have grown D. larger D. necessary D. haven't D. An idea D. higher D. be D. take D. unless D. in |