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I gave my students this multiple choice question: An unbalanced equation for the reaction of methane gas (CH_{4}) with oxygen is shown below. CH_{4} + \Box O_{2} -> 2CO_{2} + 4H_{2}O How many molecules of oxygen gas (O_{2}) are needed to properly balance this equation?

Only one answer is correct among these 4 choices:
- 1
- 2
- 3
- 4

Could you tell me which one is correct?

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