hydrogen

[joeajay7]

if i want to seperate hydrogen from air by any mechanical means without any expence how can i do it

[jake-the-peg]

Pretty easy - it's much lighter

Any uptuned vessel with a tap at the top - I'm sure you can work out the details

[chakka35]

How much hydrogen have you got in that particular air sample of yours?

[Teddio]

Is this a mixture? Repeated diffusion through a porous membrane will eventually result in fairly pure hydrogen gas. Hydrogen molecules have a much greater mean square speed than air molecules so their rate of diffusion will be greater.

[Bert]

In case you didn't realise, chakka asked his question because there is hardly any hydrogen in the atmosphere. It is so light that any that is formed will rise to the edge of the atmosphere and then carry on into space.
You can separate (note the correct spelling) the gases in the air by cooling (a lot). Hydrogen would be the last to liquefy (apart from helium, of which there isn't a lot in the atmosphere either, for the same reason) at -259 deg C.
You cannot do it without expense (note the correct spelling), because you'll need to buy or rent the equipment.

[jake-the-peg]

This is true.

Personally I was working on the assuption that it was a homework question.

So I guess it depends.