JEE Main · 2019 · Shift-IIeasyMOLE-102

The percentage composition of carbon by mole in methane (CH4) is:

Some Basic Concepts (Mole Concept) · Class 11 · JEE Main Previous Year Question

Question

The percentage composition of carbon by mole in methane (\ceCH4\ce{CH4}) is:

Options
  1. a

    75%75\%

  2. b

    20%20\%

  3. c

    80%80\%

  4. d

    25%25\%

Correct Answerb

20%20\%

Detailed Solution

🧠 By mole means count atoms, not weigh them \ceCH4\ce{CH4} has 11 C and 44 H atoms — 55 atoms total. Mole percent of C is 1/51/5.

🗺️ One quick step %C by mole=11+4×100=20%.\%\,\text{C by mole} = \frac{1}{1+4} \times 100 = 20\%.

⚠️ The 75%75\% trap 75%75\% is the mass percent of carbon, not the mole percent. Many students see "%\% composition" and jump straight to mass. Read the words "by mole" — they change everything.

Answer: (b)\boxed{\text{Answer: (b)}}

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