Statements (1), (2) and (3) are correct. (1) Adsorption isotherm is a curve that expresses the variation in the amount of gas adsorbed by adsorbent with temperature at constant pressure. It fails at high pressure. (2) During adsorption, enthalpy and entropy of system are negative and ΔG must be negative, so, process is spontaneous. (3) Physical adsorption is non-specific in nature as there are more significantly strong attraction between solute and solvent. Any gas can be adsorbed on surface of solid to some extant. (4) Due to presence of strong attraction between solute and solvent, chemical adsorption is irreversible while physisorption is reversible.