一氧化碳中混有以下气体中的两种，实验测得该混合气体中含氧元素57%，则该杂质一定不可能是以下的（ ）
①CO2 ②NO ③NO2 ④N2．
A．②③
B．①③
C．①④
D．②④
二氧化碳中氧元素的质量分数=
×100%=72.8%16×2 16×2+12
一氧化氮中氧元素的质量分数=
×100%=53.3%16 16+14
二氧化氮中氧元素的质量分数=
×100%=69.6%16×2 16×2+14
氮气中没有氧元素，故氧元素的质量分数为0；
A、②③组合中一氧化氮的氧元素质量分数为53.3%，小于57%；故可能为杂质；
B、①③组合中二氧化碳和二氧化氮中氧元素的质量分数都大于57%；故不能为杂质；
C、①④组合中氮气的氧元素的质量分数为0，小于57%；故可能为杂质；
D、②④组合中二者的氧元素质量分数都小于57%，故可能为杂质；
故选B
| 用下面方框中所给短语的正确形式填空。 | |
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