题目

某主族元素R的最高正化合价与最低负化合价的代数和为6，由此可以判断A．R可能是第二周期元素B．R一定是ⅥA族元素C．R的气态氢化物比同周期其它元素气态氢化物稳定D．R气态氢化物化学式为H2R 答案：【答案】C【解析】试题分析：某主族元素R的最高正化合价与最低负化合价的代数和为6，这说明最高价是+7价，最低价是-1价，因此是氯元素。A．氯元素是第三周期元素，A错误；B．氯元素是 ⅦA族元素，B错误；C．同周期自左向右非金属性逐渐增强，氢化物的稳定性逐渐增强，则氯的气态氢化物比同周20、Today we __1__ only three lessons in the morning．The first lesson is math．It __2__ at eight o'clock and finishes at __3__ to nine．It is in Room 101．But I don't like math．Then the second lesson is my favorite __4__ --music．It starts at nine o'clock．The __5__ lesson in the morning is PE．It starts at ten __6__ ten and finishes at five to eleven．We have our lunch at eleven thirty __7__ the second floor of dining hall．We have two lessons __8__ lunch．Art starts at two and at three o'clock we have a __9__ lesson．We can learn a lot of knowledge about China．At about four in the afternoon __10__ is over． 1．A．have                      B．has                      C．having                   D．to have 2．A．start                      B．starts                   C．is start                   D．starting 3．A．fifteen                     B．a quarter              C．quarter                   D．quarters 4．A．subjects                  B．a subject              C．subject                   D．song 5．A．last                       B．first                     C．one                        D．a 6．A．by                         B．from                    C．in                          D．past 7．A．in                   B．at                        C．on                         D．for 8．A．after                      B．before                  C．at                          D．for 9．A．math                     B．Chinese                C．art                         D．music 10．A．classes                B．a school               C．class                      D．schools 评卷人 得分 五、阅读理解 （每空？ 分，共？ 分）