镁及其化合物一般无毒（或低毒）、无污染，且镁原电池放电时电压高而平稳，使镁原电池越来越成为人们研制绿色原电池的关注焦点．其中一种镁原电池的反应为：x Mg+Mo3S4
MgxMo3S4．在镁原电池放电时，下列说法错误的是（ ）放电 充电
A．Mo3S4发生氧化反应
B．正极反应为：Mo3S4+2xe-=Mo3S42x-
C．Mg2+向正极迁移
D．负极反应为：xMg-2xe-=xMg2+
A、放电是原电池反应，负极反应是镁失电子发生氧化反应，正极反应物质是Mo3S4，得到电子发生还原反应，故A错误；
B、正极反应物质是Mo3S4，得到电子发生还原反应，正极电极反应为：Mo3S4+2xe-=Mo3S42x-，故B正确；
C、负极生成镁离子，Mg2+向正极迁移，故C正确；
D、负极反应是镁失电子发生氧化反应；负极电极反应为：xMg-2xe-=xMg2+，故D正确；
故选A．
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