更多"Learnabout Noble Gases（惰性气体）
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[单项选择]Learn about Noble Gases(惰性气体)
1. Have you ever ridden on a balloon Many tourist spots offer balloon rides in order for people to see the beauty of a place from above. A balloon contains a noble gas called helium. Formerly, balloons contained hydrogen but hydrogen is very flammable and dangerous when uncontrolled. Therefore, people shifted to helium, which is safer. Helium is safe because it has the properties of the noble gases.
2. People once believed that noble gases couldn’t chemically react at all. For this reason, they were called inert gases. They were also clustered under Group 0 in the old periodic table because scientists believed that the gases have zero valence electrons in their outer shell. This was later proven to be untrue when some noble gas compounds were discovered.
3. The gases are elements, which share similar properties. These properties include being monoatomic, colorless, odorless, being able to conduct electricity, and having low chemical reactivity. Noble ga
[单项选择]在爆炸性混合气体中加入惰性气体，当惰性气体的浓度增加到某一数值时( )
A. 爆炸上、下限差值为常数，但不为0
B. 爆炸上、下限趋于一致
C. 爆炸上限不变，下限增加
D. 爆炸下限不变，上限减小
[多项选择]钨极（不熔化极）惰性气体保护焊常用的惰性气体有（）。
A. 氩气
B. 氯气
C. 氦气
D. 氨气
[多项选择]用惰性气体作置换介质时，必须保证惰性气体用量，一般为被置换介质容积的( )倍以上。
A. 2
B. 3
C. 4
D. 5
[简答题]Describe one important thing you have ever learnt in your childhood. Include reasons and details to support your response.
[多项选择]气体保护电弧焊中，钨极惰性气体保护焊的优点包括（）。
A. 可焊有色金属、不锈钢等各种合金
B. 适用于超薄板材料焊接
C. 可进行各种位置的焊接
D. 熔敷速度快，生产率较高
