The molecular formula of methane (CH4) tells us that one molecule of methane contains one carbon atom and four hydrogen atoms. The atomic mass of carbon is approximately 12 atomic mass units (amu), while the atomic mass of hydrogen is approximately 1 amu. Therefore, the molar mass of methane is (1 x 12 amu) + (4 x 1 amu) = 16 amu.
In one molecule of methane, the mass of carbon is 12 amu, while the total mass of the molecule is 16 amu. Therefore, the weight percent of carbon in methane is:
$$(12 \text{ amu} / 16 \text{ amu}) \times 100 = 75.0\%$$
Hence, the weight percent of carbon in CH4 is 75.0%.
