问题 选择题

镭是元素周期表中第7周期第IIA族元素,下列有关叙述不正确的是

A.镭的金属性比钙弱

B.单质能与水反应生成H2

C.镭在化合物中呈+2价

D.碳酸镭难溶于水

答案

答案:A

题目分析:镭是元素周期表中第七周期第IIA族元素,与Mg、Ca等金属位于同一主族,性质相似,则A、同主族元素从上到下元素的金属性逐渐增强,因此镭的金属性比钙强,故A错误;B、钙能和水反应生成氢气,镭的金属性强于钙,因此也能与水发生反应生成氢气,故B正确;C、第IIA族元素最外层有2个电子,化合价为+2价,故C正确;D、同主族元素对应的单质或化合物的性质具有相似性,根据碳酸镁、碳酸钙的溶解性难溶可知,碳酸镭难溶于水,故D正确,答案选A。

材料分析题
单项选择题

In a recent survey, Garber and Holtz concluded that the average half-hour children’s television show contains 47 violent acts. When asked about the survey network television executive Jean Pater responded. "I sure as heck don’t think that Bugs Bunny’s pouring a glass of milk over a chipmunk’s head is violence. " Unfortunately, both Garber and Holtz and Pater beg the question. The real issue is whether children view such acts as Violence.

The violence programming aimed at children almost always appears in the context of fantasy. Cartoon violence generally includes animation, humor, and a remote setting. There is no evidence of direct imitation of television violence by children, though there is evidence that fantasy violence can energize previously learned aggressive response such as a physical attack on another child during play. It is by no means clear, however, that the violence in a portrayal is solely responsible for this energizing effect. Rather, the evidence suggests that any exciting material can trigger subsequent aggressive behavior and that it is the excitation rather than the portrayal of violence that instigates or energizes any subsequent violent behavior. "Cold" imitation of violence by children is extremely rare, and the very occasional evidence of direct, imitative associations between television violence and aggressive behavior has been limited to extremely novel and violent acts by teenagers or adults with already established patterns of deviant behavior. The institutional effect means, in the short term, that exposure to violent portrayals could be dangerous if shoaly after the exposure (within 15 to 20 minutes), the child happens to be in a situation that calls for interpersonal aggression as an appropriate response, for example, an argument between siblings or among peers. This same institutional effect, however, could be produced by other exciting but nonviolent television content or by any other excitational source, including, ironically, a parent’s turning off the set.

So there is no convincing causal evidence of any cumulative instigational effects such as more aggressive or violent dispositions in children. In fact, passivity is a more likely long term result of heavy viewing of television violence. The evidence does not warrant the p conclusions advanced by many critics who tend to use television violence as a scapegoat to draw public attention away from the real causes of violence—causes like abusive spouses and parents and a culture that celebrates violence generally.

As the evidence shows, who would most likely imitate TV violence().

A. The children who are the only child of the family.

B. The children who are extraordinarily imaginative.

C. The children who like to act against the rules.

D. The children who like fantasy TV programs.