题干

如图四条曲线分别表示ⅣA、VA、ⅥA、ⅦA族元素的气态氢化物的沸点,曲线A、B、C、D表示的气态氢化物(写化学式)分别是  ____,  ____,  ____,  ____,同一族中第3、4、5周期元素的气态氢化物沸点依次升高,其原因a ____.曲线A、B、C中第2周期元素的气态氢化物的沸点显著高于第3周期元素气态氢化物的沸点,其原因b ____

上一题 下一题 0.0难度 选择题 更新时间:2019-03-08 04:25:36

答案(点此获取答案解析)

H2O,HF,NH3,CH4,\u540c\u4e00\u65cf\u4e2d\u7b2c4\u30015\u5468\u671f\u5143\u7d20\u6c14\u6001\u6c22\u5316\u7269\u90fd\u4e0d\u542b\u6c22\u952e\u4e14\u5206\u5b50\u95f4\u4f5c\u7528\u529b\u5927\u4e8e\u7b2c\u4e09\u5468

同类题1

阅读理解

When settlers (移民)came to America during the 1600s, they were surprised to find so many trees. Some trees were so huge that a large man could not put his arms around them. Those trees helped the settlers a lot. They were glad and thankful to have these trees. They used them to build houses and make fire. From the wood of the trees, they made furniture, tools and so on.

Most people thought the forests would last forever. However, by 1800, America had its first wood shortage (短缺). How did it happen? People had not known that trees were being cut down faster than new ones could grow.

Some American people made trips to foreign countries. There they saw destroyed forests and learnt the importance of protecting forests. They came back to the United States and warned that if Americans didn’t use trees more carefully and wisely, someday the forests would all be gone. However, people were not ready to listen. Years went by, and America’s forests kept disappearing. It made some people really worried. But they did nothing.

Finally, J. Sterling Morton, the man who is remembered as the father of Arbor Day (过节), got people to listen. He named a Tree-Planting Day, or Arbor Day. He worked hard to make Arbor Day a national holiday. On that day, people usually plant a lot of trees.

Today, millions of trees have been planted in the United States because of Arbor Day. Arbor Day is such a good idea that many other countries now also have Arbor Day. Many, many trees are being planted all over the world because of J. Sterling Morton’s work.