设NA代表阿伏加德罗常数的值，下列说法正确的是( )。 A．1

搜题请搜索小程序“爱下问搜题”

问题选择题

设N_A代表阿伏加德罗常数的值，下列说法正确的是(　　)。

A．1 mol甲基(—CH₃)中含有的电子数为7N_A

B．25 ℃时，pH＝7的NH₄Cl和NH₃·H₂O的混合溶液中，OH^－数为10^－⁷N_A

C．42 g丙烯中含有的共价键数目为9N_A

D．两份均为2.7 g的铝样品分别与100 mL浓度均为2 mol·L^－¹的盐酸和氢氧化钠溶液充分反应，转移的电子数均为0.3N_A

答案

答案：C

1 mol甲基中含有电子数为9N_A，故A错误。B选选中未指明溶液的体积，无法计算OH^－的数目，B错误。丙烯的结构式为，故C正确。2.7 g铝与100 mL 2 mol·L^－¹的盐酸反应时，盐酸的量不足，转移电子数为0.2N_A，故D错误。

阅读理解

阅读下面短文，然后完成文后的任务。

Paul is a tall and heavy man. He is from America and now he lives in China. He likes Chinese food

very much. For breakfast, he has an egg, some chicken and porridge. For lunch, he eats a large blow of

noodles and some soup. For dinner,he likes dumplings and an apple. Dumplings are his favorite food.

But he can't make them. Every day he buys some (a)____ from House of Dumplings after work. He also

likes tea. He often has some (b)____ after dinner.

A) Paul 早、中、晚的饮食情况怎么样？根据短文内容，将A-H 分别填入正确的位置。

1. in the morning ____

2. at noon (中午)____

3. in the evening ____

A B C D

E F G H

B) (a)和(b)中应分别填入4._____ 和5._____.

A. tea

B. dumplings

C) 判断下列句子的正（√）误（×）。

( ) 6. Paul is of medium height.

( ) 7. Paul thinks Chinese food is great.

( ) 8. Paul's favorite food is dumplings.

( ) 9. Paul often has tea before dinner.

( ) 10. Paul is from the USA.

单项选择题

电源设备主要是给传输设备、基站收发信台提供（）的直流电源。

A、440V

B、45V

C、220V

D、48V