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?

  Options: 
 A. 1
 B. 2
 C. 3
 D. 4 
Answer: D