题干

金属铈(58Ce)常用于制作稀土磁性材料,可应用于制造玻璃、打火石、陶瓷和合金等.已知:Ce4++Fe2+═Ce3++Fe3+.下列说法正确的是(   )

A:可用电解熔融CeO2制取金属铈,铈在阳极生成

B:58138Ce、58142Ce是同素异形体

C:铈能溶于HI溶液,发生反应的离子方程式为:Ce+4H+═Ce4++2H2

D:铈的原子核外有58个电子

上一题 下一题 0.0难度 选择题 更新时间:2016-07-14 02:32:25

答案(点此获取答案解析)

D

同类题2

阅读理解

    Fear may be felt in the heart as well as in the head, according to a study that has found a link between the cycles of a beating heart and the chance of someone feeling fear.

    Tests on healthy volunteers found that they were more likely to feel a sense of fear at the moment when their hearts are contracting(收缩)and pumping blood around their bodies, compared with the point when the heartbeat is relaxed. Scientists say the results suggest that the heart is able to influence how the brain responds to a fearful event, depending on which point it is at in its regular cycle of contraction and relaxation.

    Sarah Garfinkel at the Brighton and Sussex Medical School said: “Our study shows for the first time that the way in which we deal with fear is different depending on when we see fearful pictures in relation to our heart.”

    The study tested 20 healthy volunteers on their reactions to fear as they were shown pictures of fearful faces. Dr Garfinkel said, “The study showed that fearful faces are better noticed when the heart is pumping than when it is relaxed. Thus our hearts can also affect what we see and what we don't see and guide whether we see fear.”

    To further understand this relationship, the scientists also used a brain scanner(扫描仪)to show how the brain influences the way the heart changes a person's feeling of fear.

    “We have found an important mechanism by which the heart and brain ‘speak' to each other to change our feelings and reduce fear,” Dr Garfinkel said.

    “We hope that by increasing our understanding about how fear is dealt with and ways that it could be reduced, we may be able to develop more successful treatments for anxiety disorders, and also for those who may be suffering from serious stress disorder.”

同类题3

回答下列关于草原生态系统的问题.

(1)草原上不同地段上分布着种类和密度不同的牧草,在水平方向上它们通常呈____ 分布.草原上的植被能防风固沙、保持水土,对于缓解相邻地区的沙尘天气有一定的作用,这体现了生物多样性的____ 价值.

(2)蝗灾已成为草原农牧业生产的重大危害之一.图甲示研究者对草原上四种主要蝗虫密度对牧草产量(牧草产量=牧草补偿量一蝗虫取食量)影响的实验结果;图乙为农业部门对某次“亚洲小车蝗”的爆发和防治过程中种群密度的调查结果.

①由图甲可知,该实验的因变量是____ ,甲图所示结果为研究者依据实验结果建立的____模型.当狭翅雏蝗密度为5头/m2时,牧草产量增加,原因是____,说明蝗虫只有达到一定量才会导致危害,因为生态系统具有____ .

②若图乙是对蝗虫的幼虫跳蝻进行调查所获得的结果,则该调查采用的方法是____ .为探究治理蝗灾的最好措施,农业工作者在蝗灾期间,分别采用了农药防治和生物防治的方法.由图乙可知,图中____ 点是进行了农药防治,随农药使用次数的增多防治效果变差;图中____ 点是引入害虫的天敌进行生物防治,利用生物间的____ 等种间关系,使防治效果持久而稳定.

(3)严重的草原火灾会破坏生态系统,但适当的“地面火”能烧掉枯枝落叶,加速生态系统的____ ,还可使部分位置获得更多光线,促进植物的光合作用,利于植被生长.火灾后的草原演替的过程中,生物种类、数量及有机物含量的变化趋势是____ (填“增加”、“减少”或“不变”).