有三瓶无色无味的气体，分别是氧气、空气、二氧化碳，区别它们最简单的方法是（ ）
A．测定气体的密度
B．伸入带火苗的木条
C．滴入澄清石灰水，振荡
D．滴入紫色石蕊试液，振荡
答案：B
题目分析：区别空气、氧气和二氧化碳三瓶无色气体，要求根据三种气体性质差别，所设计的方案能出现三种明显不同的实验现象，达到鉴别气体的目的．
解：A、三种气体密度不同，测三瓶气体的密度可以区别三种气体，但不是最简单方法；故A错误，
B、燃着的木条分别放入瓶中，燃烧无明显变化的气体为空气；燃烧更旺的气体为氧气；燃烧熄灭的气体为二氧化碳；故B正确，
C、倒入澄清石灰水，石灰水变浑浊的气体为二氧化碳，无明显现象的为空气或氧气．无法区别三种气体，故C错误，
D、倒入紫色石蕊试液，使溶液变红的气体为二氧化碳，无明显现象的为空气或氧气．无法区别三种气体，故D错误，
故选B．
点评：利用所要鉴别物质的性质差别，设计实验，实验中出现明显的现象差异，达到鉴别物质的目的．
请阅读下列的相关信息，并按照要求匹配信息。请在答题卡上将对应题号的相应选项字母涂黑。 以下是6条有关颜色偏好和性格关系的描述。 A
小题1:Create a warm and personal working atmosphere; establish a peaceful working environment and try to avoid conflict(冲突); allow them freedom to express their feelings; Praise them for their creativity. 小题2:Assign them work needing detailed planning; define the tasks in clear terms; provide a stable work environment and avoid sudden change; issue rules and regulations; provide good examples. 小题3:Assign them work which needs analytical thinking and problem-solving skills; encourage them to think independently and take their ideas to the next step. 小题4:Assign them work which is action-packed; provide opportunities which need skills and challenges; do not let them do the same job for a long time. 小题5:Assign them work which needs full energy; provide competitive opportunities; let them know that they will be promoted if they do brilliantly. |