Explain why during the early part of the nineteenth century

Explain why, during the early part of the nineteenth century, a number of gases (CO2, SO2, etc) could be liquefied whereas others (O2, H2, etc) could not be liquefied, despite attempts using pressure up to 3000 atm

Solution

critical temperature of CO2 and SO2 are respectively 304.2K and 430.5K So they can be easily liquified. On the contrary O2 and H2 have critical temperature of 154. 6K and 33.2K. Both the temperatures being well below room temperature, can not be liquified if unless cooled below critical temperatures, whatever the pressure may be. As. liqid nitrogen came in and better cooling techniques were invented people were able to go to below critical temperature of H2 and liquify those gases.