Question

Give reasons: ​
Hydrogen is collected by the downward displacement of water and not of air, even though it is lighter than air.​

Answer 1

Hydrogen is collected by downward displacement of water because hydrogen is insoluble in water, so it does not dissolve in water to form any compounds.​ ​

Hydrogen cannot be collected by downward displacement of air even though it is lighter than it because it forms an explosive mixture with oxygen present in the air. ​