题干

具有下列电子层结构的原子,其对应元素一定属于同一周期的是

A:两种原子的最外电子层上全部都是s电子

B:3p能级上只有一个空轨道的原子和3p能级上只有一个未成对电子的原子

C:最外层电子排布为2s22p6的原子和最外层电子排布为2s22p6的离子

D:M层上的s能级和p能级都填满了电子,而d轨道上尚有电子的两种原子

上一题 下一题 0.0难度 选择题 更新时间:2017-11-23 09:53:56

答案(点此获取答案解析)

B

同类题3

阅读理解

    There is an old saying about volunteer work that goes like this: “ No one can do everything, but everyone can do something.”

    Today, many people volunteer their time and energy to help others. There are a lot of ways to meet other people's needs. For example, some volunteers provide help after a disaster. Others are happy to get dirty while repairing homes or planting trees or flowers in poor neighborhoods. Young people see suffering and loneliness around them and find ways to help. And history lovers help archeologists(考古学家) search for ancient objects to help deepen our knowledge of the past.

    Volunteers work in many areas around the world, including Haiti. More than four years have passed since a 7.0 earthquake shook the nation. The exact number of people who died may never be known. Thousands of survivors of the Haitian earthquakes still live in temporary shelters. Last year, former American President Jimmy Carter and his wife Rosalynn joined five hundred volunteers in the town of Leogane to build houses.

    Organizations do not have to be large to get volunteers. An activist group in Dharamsala, India is a good example, Jodie Underhill from England arrived in northern India several years ago. She planned to volunteer for an environmental project. She could almost not believe how much rubbish was ruining some of the area's most beautiful sights. Jodie Underhill learned about how to deal with the rubbish while taking part in other volunteer projects. But soon enough she formed her own group, Mountain Cleaners. Jodie Underhill says the work is very hard. But she praises the group's efforts as a wonderful experience. The young Englishwoman says the Indian media started calling her “Garbage Girl”. And she says she was pleased with the name.

    American teenagers also volunteer in many ways .