Regarding the chemical reactivity, the maximum hardness principle states stable systems are associated with a relatively higher molecular hardness . The PhosO nanoadsorbents display a similar molecular hardness compared to intrinsic phosphorene (η=0.6-0.7 eV), denoting that the oxidation almost does not affect the chemical stability of phosphorene. Also, μ is related to the electronegativity χ through μ=-χ; while ω is the gained stability when the molecular system gains electrons. Hence, μ and ω are related to the relative electrophilic character . Due to the oxidizing groups, the PhosO electrophilic character is slightly increased compared to phosphorene (μ=-4.4 eV; =15.2 eV). Note that the and the electron acceptor character increases drastically. Thus, highly oxidated phosphorene has high reactivity, turning it chemically unreliable for practical applications. In other words, highly oxidated phosphorenes will be easily converted to lesser O:P ratio systems through reduction reactions due to its strong acceptor character.