easy u

3.to use a measuring cylinder to meeasure the volume of a bottle of distilled water,which of the following is incorrect?
a.the cylinder should be placed vertically
b.to fix its position by holding the middle part of the cylinder
c.bend down and look at the bottem of the curved surface of the liquid

d.the cylinder should be dried before pouring distilled water into it
The answer is D.
Water in the measuring cyclinder would not affect the volume.


4.when there is striking back,we should
a.complete the experiment immediately
b.blow out the flame
c.close the air hole
d.turn off the gas tap
The answer is C.
開本生燈時唔關氣孔，就會令到氣孔有煤氣泄漏，
再與空氣中的氧混合，燃點時就會連氣孔也會有火，
這稱為"回擊現象"，是實驗的大忌

若果不快速處理這現象，
本生燈的溫度過高，會引致爆炸，
本生燈的碎片會可能傷及四周的人。
So, close the air hole, 防止煤氣泄漏..

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