在一定温度的定容密闭容器中，反应A2（g）+B2（g）
2AB（g）达到平衡状态的是（ ）
A．混合气体的密度不再改变
B．容器内的总压强不随时间而变化
C．单位时间内生成2nmolAB的同时，生成nmol的B2
D．A2、B2、AB的分子数之比为1：1：2时
A、根据质量守恒，化学反应前后混合物的质量不变，容器体积不变，所以密度始终不变，故A错误；
B、该反应前后气体体积不变，所以压强始终不变，故B错误；
C、位时间内生成2nmolAB的同时，生成nmol的B2，说明正逆反应速率相等，所以达到平衡状态，故C正确；
D、反应达到平衡时的浓度与反应的初始物质的量以及反应的转化程度有关，所以不能确定是否达到平衡，故D错误；
故选C．
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