题目

  The fourth of July marks the anniversary of America’s Declaration of Independence from Britain. During the summer of 1776, American colonists were deeply divided. Almost one in three was loyal to Britain. Yet most were increasingly angry about what they considered unfair treatment by the British government. By June, fighting had already taken place between colonial forces and Britain. The idea of independence was spreading.    Delegates (代表) from the thirteen colonies gathered in Philadelphia, Pennsylvania. The Continental Congress decided that a document declaring separation 下图是氧元素、铝元素在周期表中的位置及有关的结构示意图：    回答下列问题： （1）铝元素的原子序数为             ；属于铝离子的结构示意图是            （填序号，下同）； （2）右图中属于氧原子的结构示意图的是            ； （3）氧元素与铝元素最本质的区别是             ； A．中子数不同   B．质子数不同 C．相对原子质量不同 D．电子数不同  （4）甲、乙两种元素组成的化合物的化学式为             。