4) If the kettle of liquid air were placed over a lighted Bunsen burner, frost and ice would collect on the bottom of the kettle. - второй тип (Conditional II)
5) A red hot rod of steel would have burned brilliantly if had been placed in the liquid air. - третий тип (Conditional III)
6) If the relative humidity were low, evaporation would occur rapidly. -
второй тип (Conditional II)