题目

已知R2－离子的核内有n个中子，R的质量数为M，则mgR2－离子里含有电子的物质的量为（ ）A. B. C. D. 答案：【答案】D【解析】由R2-的核内有n个中子，R的质量数为M，则质子数为M-n，故R2-阴离子的核外电子数为M-n+2，mg R2-的物质的量为mol，所以mgR2-阴离子含有的电子的物质的量为×（M-n+2）=。答案：D Our class ________ forty-five students, in other words, forty-five students ________ our class． [　　] A． consists of, are made up of B． is consisted of, make up C． consists of, make up D． is consisted of, are made up of