Hard X-ray Photoelectron Spectroscopy (HAXPES) measurements at various potentials and reported that for a sample with a size distribution centered around 2.6 nm, only the outer platinum shell was oxidized. The presence of oxygen atoms near the center of the nanoparticle in our simulation is justified by the nature of the Monte Carlo simulations which disregard kinetic aspects. Hence, atomic rearrangement required for oxygen to penetrate deep into the core is bypassed i.e. no activation energy of oxygen diffusion into the platinum lattice, which otherwise, renders this process kinetically unfavorable. Our experimental evidence along with previous experimental work, suggests that the size range between 1.5 nm and 2.5 nm represents a critical transition region where the oxidation behavior changes dramatically. Within this narrow size window, nanoparticles appear to shift abruptly from partial surface oxidation to complete oxidation, indicating a sharp threshold effect. The precise point of this shift likely depends on specific experimental conditions such as temperature, type of oxidant and partial pressure. Furthermore, the presence of defects or strain in the nanoparticles, which can vary based on synthesis methods may have an influence as well.