在如图所示的装置中，a的金属性比氢要强，b为碳棒，关于此装置的各种叙述不正确的是（ ）
A．碳棒上有气体放出，溶液酸性变弱
B．a是负极，b是正极
C．导线中有电子流动，电子从a极到b极
D．a极上发生了还原反应
答案：D
在原电池中较活泼的金属作负极，失去电子，发生氧化反应。电子经导线传递到正极上，所以溶液中的阳离子向正极移动，阴离子向负极移动。正极得到电子，发生还原反应。所以a电极是负极，失去电子，发生氧化反应，b电极是正极，所以选项D是错误的，其余选项都是正确的，答案选D。
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certain methods and procedures to obtain new knowledge and greater understanding. Although the methods are not always the same, there are usually certain elements in the procedures that are similar. 1. （ ） Problems must first of all be recognized. The right answers can be obtained only if the right questions are asked. A thoroughly understood problem is well started toward solution. Problems arise in a variety of ways. Sometimes they grow out of a chance observation. They may result from reading, from laboratory experiments, or simply from thinking. They also may result from new developments or from new or different human needs. Today, for example, problems are arising from new discoveries in the fields of nuclear physics, biological engineering and microelectronics. The development of industry has also brought about large numbers of problems which have to be solved. 2. （ ） Next, the scientist tries to learn as much as possible about it. Often this means going to the library and studying books which contain accounts of man's experience and knowledge of the problem. This is called searching the literature. The scientist may find that others have already solved all or a part of the problem. Occasionally he finds answers to closely related questions, which give clues for solving the new one. In his search the scientist accumulates much background information. With these new ideas and facts he builds a firm foundation for solving the problem. 3. （ ） After the scientist has finished this part of his work he will probably take the many facts which he has collected and organize them into some kind of system. This may be a logical classification or it may be a mathematical analysis. Usually the analysis will show unanswered questions. Sometimes it will suggest areas that are in need of further study. Perhaps one of the most important results of such an analysis is that it indicates certain truths, which generally are called inferences. 4. （ ） In making an inference the scientist has built up a hypothesis. A hypothesis is only a"best" guess. It must next be tested. If it is correct, the certain things should follow. This means if a particular experiment is carried out, certain observation ought to be possible or it should be possible to make certain predictions. Should the observations or predictions turn out to be as expected, the scientist has added confidence in the probable truth of his hypothesis. If, however, observations cannot be made or the predications are unreliable, then the hypothesis will probably be given up or at least modified. 5. （ ） The hypothesis must check with the facts. Scientific facts are usually established by work in the laboratory. Experiments have to be made under carefully controlled conditions. Thorough and accurate records must be kept. In making certain kinds of experiments in science variables are used. A variable is something which has different values under different conditions. In one type of laboratory test all the variables but one are controlled. This method of testing is called controlled experimentation. |