Although hydrogen is lighter than air it is not collected by the downward displacement of air.Why?

Although hydrogen is lighter than air it is not collected by the downw

1.	Although hydrogen is lighter than air it is not collected by the downward displacement of air.Why?
Answer» Hydrogen gets oxidised when it is exposed to oxygen which makes it burn with a pale blue FLAME and the RESIDUE is water. This means that it mixes with oxygen. DOWNWARD DISPLACEMENT of air requires a gas that does not mix with air and is lighter than air. Hydrogen is lighter than airbut mixes with air.