Which gas would impact the O2 reading by dilution when humidity increases?

When humidity increases, water vapor in the air can displace other gases present in the environment. The oxygen reading can be impacted by dilution because the increase in water vapor leads to a higher total gas composition without a corresponding increase in the actual concentration of oxygen.

In a humid environment, the partial pressure of each individual gas, including oxygen, is altered due to the presence of water vapor, which does not contribute to the oxygen measurement. Essentially, the presence of moisture means that the same volume of air now contains less oxygen in terms of its percentage composition because some of that volume is occupied by water vapor. Therefore, when humidity rises, the effective concentration of oxygen can appear lower due to this dilution effect, impacting the O2 reading.

Carbon monoxide, methane, and nitrogen dioxide, while they can affect measurements in various ways, do not cause a dilution effect on oxygen readings directly through humidity. Their influence is typically related to toxicity or specific chemical reactions rather than a direct impact from the presence of water vapor in the air. Thus, the correct answer highlights the unique way that humidity alters the reading of oxygen by directly affecting its concentration through dilution.