Explain Dalton's Law of Partial Pressures.

Dalton's Law of Partial Pressures states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the individual pressures exerted by each gas in the mixture, when measured in the same volume and temperature conditions. Each gas in the mixture behaves independently and contributes its own partial pressure to the total pressure.

This law can be mathematically expressed as:

[ P_{\text{total}} = P_1 + P_2 + P_3 + ... + P_n ]

where ( P_1, P_2, P_3, ) and so on represent the partial pressures of the individual gases in the mixture.

In this context, the reason the correct choice is the one stating that the total pressure equals the sum of the pressures of all gases is rooted in the principle of independence of gas molecules in a mixture. Each gas exerts pressure as if it occupies the entire volume alone, allowing their effects to be additive.

The other options do not accurately represent the principle outlined in Dalton's Law. While one choices mention an average pressure or lowest pressure which do not apply here, another incorrectly involves partial volumes, which is a different concept related to the behavior of gases.