下列物质的变化属于物理变化的是（）

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下列物质的变化属于物理变化的是（）

A：火烧赤壁

B：干冰升华

C：淀粉水解

D：铁钉生锈

上一题下一题 0.0难度选择题更新时间:2016-09-14 12:56:50

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B

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    Liu Yun, 13, pretty and smart. She is a good student. But many students try to stay away from her because Liu Yun's mum has AIDS(爱滋病) and her father has died of AIDS. Luckily, Liu Yun didn't get it.
    AIDS means fear for most people. Nobody wants to play games with her. Even a teacher who used to like her turns his back on her now. The biggest problem is how other people look at her. She sometimes wants todrop out of schoolbecause she can no longer face others' indifference(冷漠)。
    It is said if a person has AIDS, it's still safe to eat and play with him. So I think Liu Yun's classmates and teachers are afraid of AIDS because they don't know much about AIDS. And Liu Yun needs their love and understanding. Even a friendly smile means a lot to her.

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两种硫酸盐按一定比例混合后共熔，可制得化合物X，X溶于水能电离出K^＋、Cr³⁺、SO₄²^－，若将2．83 g X

中的Cr³⁺全部氧化为Cr₂O₇²^－后，溶液中的Cr₂O₇²^－可和过量KI溶液反应，得到3．81g I₂，反应的离子方程式为：Cr₂O₇²^－＋I^－＋H^＋→Cr³⁺＋I₂＋H₂O（未配平）。若向溶有2．83 g X的溶液中，加入过量的BaCl₂溶液，可得到4．66 g白色沉淀．由此可推断出X的化学式为

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