the conc=mass/vol can be used for both solution and gas?

Yeap definitely
Only for volume then thrs a diff
Eg: 1 mol of Cl2 occupies 24dm3
Hence if i have 48dm3 of Cl2 i wld have 48/24=2 mol of Cl2
If i have 48g of Cl2 then i wld have 48/71 mol of Cl2

so if they give the max level of chlorine gas in volume instead of concentration then the formula cant be used?

Yeap cnt

Note:if they ask for number of molecules u always need to find number of moles first then multiply by avogadros constant 6x10^23
If they ask for number of atoms
Because Cl2 itself is a molecule and there are 2 Cl atoms chemically combined
So the number of moles of molecules multiply 2 is number of moles of atoms
(For qns that ask for number of atoms)
-take note of this
Hence in this case
To find number of moles using conc u need find the mass first since thats what they gave u.so 0.005x10^3 x1dm^3 then divide by relative molecular mass which is 71
If they give vol— to get number of moles from vol of GAS u divide by 24dm3

ok thx for helping me with this qn :>

The presentation looks off...

You cannot use the word "mole" as an abbreviation of "molecule". These are two distinct terms even though "mole" seems to be a shortened form of "molecule".

Oh yup i wrote it wrong,thanks for the correction:)