搜题请搜索小程序“爱下问搜题”
问题 选择题

下列化学式书写规范的是                （    ）

A．氧化镁mgO

B．氯化铝alCl3

C．五氧化二磷P2O5

D．一氧化碳CO

答案

答案：C

本题考查化学用语的意义及书写，解题关键是分清化学用语所表达的对象是分子、原子、离子还是化合价，才能在化学符号前或其它位置加上适当的计量数来完整地表达其意义，并能根据物质化学式的书写规则正确书写物质的化学式；注意化学式中字母的书写（大小写）．

A、氧化镁mgO，元素符号的书写注意“一大二小”，改为“MgO”，故A错误；

B、元素符号的书写注意“一大二小”，则改为：氯化铝AlCl3，故B错误；

C、五氧化二磷P2O5，化学式书写规范，故C正确；

D、一氧化碳Co中，氧元素的元素符号书写错误，改为“CO”，故D错误．

故选C．

选择题

某反应为2X+3O2

 点燃 
.
 
2CO2+4H2O，根据质量守恒定律则X的化学式是（　　）

A．H2

B．CH4

C．CH4O

D．C2H6O
查看答案
单项选择题

Comparisons were drawn between the development of television in the 20th century and the diffusion of printing in the 15th and 16th centuries. Yet much had happened between. As was discussed before, it was not until the 19th century that the newspaper became the dominant pre- electronic (61) , following in the wake of the pamphlet and the book and in the (62) of the periodical. It was during the same time that the communications revolution (63) UP, beginning with transport, the railway, and leading on through the telegraph, the telephone, radio, and motion pictures into the 20th-century world of the motor car and the air plane. Not everyone sees that process in (64) . It is important to do so.

It is generally recognized, (65) , that the introduction of the computer in the early 20th century, (66) by the invention of the integrated circuit during the 1960s, radically changed the process, although its impact on the media was not immediately (67) . As time went by, computers became smaller and more powerful, and they became "personal" too, as well as (68) , with display becoming sharper and storage (69) increasing. They were thought of, like people, (70) generations, with the distance between generations much (71) .

It was within the computer age that the term "information society" began to be widely used to describe the (72) within which we now live. The communications revolution has (73) both work and leisure and how we think and feel both about place and time, but there have been (74) view about its economic, political, social and cultural implications. "Benefits" have been weighed (75) "harmful" outcomes. And generalizations have proved difficult.

（72）是（）

A.context

B.range

C.scope

D.territory
查看答案