The correct answer is option 3: Nitrogen.

When potato chips are packaged, they are often flushed with nitrogen gas. This process helps to prevent rancidity, which is the spoilage of fats and oils in the chips that can lead to an unpleasant taste and odor.

Option 1: Carbon dioxide is not typically used to flush potato chip packets because it can react with the fats and oils in the chips, causing them to become rancid more quickly.

Option 2: Hydrogen is not used to flush potato chip packets as it is a highly flammable gas and can pose a safety hazard in packaging and storage.

Option 4: Oxygen is not used to flush potato chip packets because it can cause the fats and oils in the chips to oxidize, leading to rancidity.

In summary, nitrogen is the gas of choice for flushing potato chip packets to prevent rancidity and maintain the quality and freshness of the chips.