题目

已知元素R的某种同位素，形成离子化合物的化学式为AmRn，化合物中一个R粒子的核外电子数是a，核内中子数是b，则该同位素的原子的符号是(    )A.                  B.               C.             D. 答案：C解析：因为AmRn为离子化合物，则阴离子为Rm-，Rm-的核外有a个电子，故Rm-的质子数为a-m，中子数为b，质量数(A)=a-m+b，即答案为C。假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处错误，每句中最多有两处。错误涉及一个单词的增加、删除或修改。增加：在缺词处加一个漏词符号(∧)，并在其下面写出该加的词。删除：把多余的词用(\)划掉。修改：在错的词下画一横线，并在该词下面写出修改后的词。注意：1）每处错误及其修改均仅限一词；2）只允许修改9处，多者(从第10处起)不计分。Dear Bob,I am very exciting to receive an e-mail from you and I am glad to know you have a wonderful time during the past summer holiday. I took a trip to the countryside with some of my friend in last summer. Country life, in your opinion, gave me relaxation, which I can't enjoy in big cities. There was river nearby, in that we went swimming every now and then. You can never imagine how fun it was to swim together with friends in the cool, clean river in so hot days. In fact, I had never had a better holiday before and I took plenty of photos there. I keep the photos where I can see them every day, as they are worth keep forever.Yours,Tom