Two-dimensional ferroelectrics are important quantum materials which have found novel applications in nonvolatile memory devices, however the effects of their reversible polarization on chemical reactions and interactions with environments are rarely studied despite their importance. Here, based on first principles calculations, we found distinct gas adsorption behaviors on the surfaces of the ferroelectric In2Se3 layer and reversible gas capture and release controlled by a ferroelectric switch. We rationalize this novel phenomenon to the synergistic effect of electrostatic potential differences and electron transfer induced by band alignments between the frontier molecular orbitals of gas and the band-edge states of the substrate. Excitingly, the adsorption of paramagnetic gas molecules such as NO and NO2 can induce surface magnetism, which is also sensitive to the ferroelectric polarization direction of In2Se3, indicating the application of In2Se3 as a threshold magnetic sensor/switch. Furthermore, it is suggested that two NO molecules ferromagnetically couple with each other, leading to the Curie temperature being polarization surface dependent and it can reach up to 50 K, and long-sought 2D molecule multiferroics. The ferroelectric controllable adsorption behavior and multiferroic feature of the molecules will find extensive application in gas capture, selective catalytic reduction and spintronic devices.