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2008年北京奧運會主體育場的外形好似“鳥巢”（The Bird Nest），有一類物質也好似鳥巢，如化學式是B5H9的五硼烷（見圖）．下列有關五硼烷的說法錯誤的是（ ）

A．五硼烷屬于化合物
B．五硼烷的相對分子質量是64
C．五硼烷中硼元素和氫元素的質量比為5：9
D．1個五硼烷分子由5個硼原子和9個氫原子構成
【答案】分析：根據五硼烷的化學式和結構來回答，依據其元素組成來判斷物質的種類，計算相對分子質量和各元素的質量比時，一定不要忽略各元素的原子個數．
解答：解：A、五硼烷屬于化合物，因為里面含有兩種元素．
B、五硼烷的相對分子質量=11×5+1×9=64．
C、五硼烷中硼元素和氫元素的質量比11×5：1×9=55：9．
D、五硼烷分子由5個硼原子和9個氫原子構成．
故選C
點評：化學式中元素的質量比和原子個數比一定要分清，不要因為粗心而失分．
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