The percentage composition of carbon by mole in methane is:

• (A) 80 %
• (B) 25 %
• (C) 75 %
• (D) 20 %

To determine the percentage composition of carbon by mole in methane (CH₄), we first need to understand the molecular structure of methane. Methane consists of one carbon atom and four hydrogen atoms. Let's break this down step by step.

Understanding Molecular Composition

The molecular formula for methane is CH₄, which indicates that there is:

• 1 carbon atom (C)
• 4 hydrogen atoms (H)

Calculating the Total Number of Moles

To find the percentage composition by mole, we first calculate the total number of moles of atoms in the molecule. In methane, we have:

• 1 mole of carbon
• 4 moles of hydrogen

This gives us a total of:

Total moles = 1 (C) + 4 (H) = 5 moles

Finding the Percentage of Carbon

Next, we calculate the percentage of carbon by mole using the formula:

Percentage of Carbon = (Moles of Carbon / Total Moles) × 100

Substituting the values we have:

Percentage of Carbon = (1 / 5) × 100 = 20%

Final Answer

Thus, the percentage composition of carbon by mole in methane is 20%. Therefore, the correct answer is (D) 20%.

Why This Matters

Understanding the percentage composition of compounds is crucial in chemistry, especially when dealing with reactions and stoichiometry. It helps in predicting how substances will react and in calculating yields in chemical reactions.