`{:(,"Coloumn-I",,"Column-II"),("(a)","At low pressure",,(p)Z=1+(pb)/(RT)),("(b)","At high pressure",,(q)Z=1-a/(V_(m)RT)),("(c)","At low density of gas",,"(r)Gas is more compressible then ideal gas"),("(d)",for H_(2) and He at 0^(@) C,,"(s)Gas is less compressible than ideal gas"):}`

Answer

A-q,r ; B-p,s ; C-q,r ; D-p,s

Explanation

(A)At low pressure, b is negligible in comparison to `V_m`
`(P+a/V_m^2)(V_m)=RT`
`implies (PV_m)/(RT)=Z=1-a/(V_mRT)lt1`
So, gas is more compressible than ideal gas.
(B)At high pressure, `a/V_m^2` is negligible in comparison to P.
`:. P(V_m-b)RT`
`implies (PV_m)/(RT)=Z=1+(Rb)/(RT)lt1`
So, gas is less compressible than ideal gas.
( C)Low density of gas means pressure is low so, at low pressure `Z=1-a/(V_mRT)lt1` and gas is more compressible than ideal gas.
(D)At `0^@C H_2` and He have `a~~0`
So, `Z=1+(Pb)/(RT)` and gas is less compressible than ideal gas.