C
分析:假定該物質(zhì)為純凈物,求出Fe
2O
3中氧元素的質(zhì)量分?jǐn)?shù),與題給數(shù)據(jù)混合物中氧的含量(氧元素的質(zhì)量分?jǐn)?shù)),做比較.根據(jù)物質(zhì)中某元素的質(zhì)量分?jǐn)?shù)=
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×100%,進行解答本題.
解答:純凈的Fe
2O
3氧元素的質(zhì)量分?jǐn)?shù)為:
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×100%=30%,
題中給的數(shù)據(jù)為是氧化鐵中氧元素的質(zhì)量分?jǐn)?shù)與另一種氧化物中氧元素的質(zhì)量分?jǐn)?shù)的平均值,
由于50%>30%,所以另一種氧化物中氧元素的質(zhì)量分?jǐn)?shù)必須要大于30%、;
A、MgO中氧元素的質(zhì)量分?jǐn)?shù)=

×100%=40%,故A不符合題意;
B、Na
2O中氧元素的質(zhì)量分?jǐn)?shù)=

×100%=25.8%,故B不符合題意;
C、CO
2中氧元素的質(zhì)量分?jǐn)?shù)=
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×100%=72..7%,故C符合題意;
D、SO
2中氧元素的質(zhì)量分?jǐn)?shù)=
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×100%=50%,故D不符合題意;
故選:C.
點評:混合物成分的確定用極值法,也就是先假定該物質(zhì)為純凈物,算出相關(guān)的量,再與題給量相比較,就能得出正確的結(jié)論.