What products are obtained when CH4(g) burns completely in an excess of oxygen?

When methane (CH4) burns completely in the presence of an excess of oxygen, the primary products formed are carbon dioxide (CO2) and water (H2O). The complete combustion of methane can be represented by the balanced chemical equation:

[ \text{CH}_4(g) + 2 \text{O}_2(g) \rightarrow \text{CO}_2(g) + 2 \text{H}_2\text{O}(g) ]

In this reaction, each molecule of methane reacts fully with oxygen to produce one molecule of carbon dioxide and two molecules of water. This complete burning is typically associated with a sufficient amount of oxygen, ensuring that all the carbon in methane is oxidized to carbon dioxide rather than producing carbon monoxide (CO) or elemental carbon (C), which can occur in incomplete combustion scenarios.

Thus, the correct choice accurately reflects the complete combustion reaction of methane, where the products are carbon dioxide and water, highlighting the importance of sufficient oxygen for complete burning.