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下列一组有水参与的反应：

①2Na+2H2O=2NaOH+H2↑

②2Na2O2+2H2O=4NaOH+O2↑

③Na2O+H2O=2NaOH

④3Fe+4H2O

高温
.
Fe3O4+4H2

⑤2H2O

电解
.
2H2↑+O2↑

⑥2F2+2H2O=4HF+O2

（1）其中不属于氧化还原反应的是______（填编号）．

（2）在这些氧化还原反应中，

水只作氧化剂的反应是______（填编号）；

水只作还原剂的反应是______（填编号）；

水既作氧化剂，又作还原剂是______（填编号）；

水既不作氧化剂，又不作还原剂是______（填编号）．

（3）根据你的理解，氧化还原反应的实质是______

A．分子中的原子重新组合

B．氧元素的得失

C．电子的得失或共用电子对的偏移

D．化合价的改变

（4）请你运用所学知识分析3NO2+H2O=2HNO3+NO是否属于氧化还原反应？______（填“是”或“不是”），若是，这个反应的氧化剂是______，还原剂是______．

答案

（1）氧化钠和水的反应中，各元素化合价都不变，所以该反应属于非氧化还原反应，故答案为：③；

（2）①2Na+2H2O=2NaOH+H2↑中，水中氢元素化合价由+1价变为0价，钠元素化合价由0价变为+1价，所以水只作氧化剂；

②2Na2O2+2H2O=4NaOH+O2↑中，过氧化钠中氧元素化合价由-1价变为0价和-2价，所以过氧化钠既是氧化剂又是还原剂，水中各元素化合价不变，所以水既不是氧化剂也不是还原剂；

④3Fe+4H2O

高温
.
Fe3O4+4H2中，铁元素化合价由0价变为+2价和+3价，氢元素化合价由+1价变为0价，所以铁所还原剂，水作氧化剂；

⑤2H2O

电解
.
2H2↑+O2↑中，氢元素化合价由+1价变为0价，氧元素化合价由-2价变为0价，所以水既是氧化剂又是还原剂；

⑥2F2+2H2O=4HF+O2中氟元素化合价由0价变为-1价，氧元素化合价由-2价变为0价，所以氟气是氧化剂，水是还原剂，

故答案为：①④；⑥；⑤；②；

（3）在上述氧化还原反应中，既有电子的得失又有电子对的偏移，所以氧化还原反应的实质是电子的得失及电子对的偏移，故答案为：C；

（4）该反应中氮元素化合价由+4价变为+2价和+5价，所以该反应是氧化还原反应，且二氧化氮既作氧化剂又作还原剂，故答案为：是；NO2；NO2．

问答题

Clinical depression is a serious ailment, but almost everyone gets mildly depressed from time to time. Randolph Nesse, a psychologist and researcher in evolutionary medicine at the University of Michigan, likens the relationship between mild and clinical depression to the one between normal and chronic pain. (46)He sees both pain and low mood as warning mechanisms and thinks that, just as understanding chronic pain means first understanding normal pain, so understanding clinical depression means understanding mild depression.

Dr. Nesse’s hypothesis is that, as pain stops you doing damaging physical things, so low mood stops you doing damaging mental ones — in particular, pursuing unreachable goals. Pursuing such goals is a waste of energy and resources. (47)Therefore, he argues, there is likely to be an evolved mechanism that identifies certain goals as unattainable and inhibits their pursuit — and he believes that low mood is at least part of that mechanism.

It is a neat hypothesis, but is it true？A study published in this month’s issue of the Journal of Personality and Social Psychology suggests it might be. Carsten Wrosch from Concordia University in Montreal and Gregory Miller of the University of British Columbia studied depression in teenage girls. Their conclusion was that those who experienced mild depressive symptoms could, indeed, disengage more easily from unreachable goals. That supports Dr. Nesse’s hypothesis. (48)But the new study also found a remarkable corollary: those girls who could disengage from the unattainable proved less likely to suffer more serious depression in the long run.

Mild depressive symptoms can therefore be seen as a natural part of dealing with failure in young adulthood. (49)They set in when a goal is identified as unreachable and lead to a decline in motivation, and in this period of low motivation, energy is saved and new goals can be found. If this mechanism does not function properly, though, severe depression can be the consequence.

Dr. Nesse believes that persistence is a reason for the exceptional level of clinical depression in America— the country that has the highest depression rate-in the world. (50)”Persistence is part of the American way of life, ” he says. “People here are often driven to pursue overly ambitious goals, which then can lead to depression. ” He admits that this is still an unproven hypothesis, but it is one worth considering. Depression may turn out to he an inevitable price of living in a dynamic society.

(50)”Persistence is part of the American way of life, ” he says. “People here are often driven to pursue overly ambitious goals, which then can lead to depression. ”
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国外咨询公司的生存方式是（）。

A.用事实说话

B.用数据说话

C.用经验说话

D.用利润说话
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