X、Y、Z、W均为短周期元素，它们在周期表中的相对位置如图所示。若Y原子的最外层电子数是内层电子数的3倍，下列说法中正确的是( )。
A．只由这四种元素不能组成有机化合物
B．最高价氧化物对应的水化物的酸性W比Z弱
C．Z的单质与氢气反应较Y剧烈
D．X、Y形成的化合物都易溶于水
答案：A
根据Y原子的最外层电子数是内层电子数的3倍，可判断Y为氧元素，因此X、Z、W分别为氮、硫、氯元素。因要组成有机化合物必须含有碳、氢元素，因此A选项正确。
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