In mass spectrometry, what is the molecular ion ($M+$) formed when methane ($C_1{H}_4$) is ionized in the mass spectrometer?

• A. $C_1{H}_4-$
• B. $C_1{H}_3+$
• C. $C_1{H}_2+$
• D. $C_1{H}_4+$

Answer: (D)

Verified step by step guidance

1. Understand that in mass spectrometry, the molecular ion (M⁺) is formed by the removal of one electron from the neutral molecule without breaking any bonds, resulting in a radical cation.
2. Identify the molecular formula of methane, which is CH₄, meaning one carbon atom bonded to four hydrogen atoms.
3. Recognize that ionization in the mass spectrometer typically removes one electron from the molecule, producing the molecular ion with the same atomic composition but a positive charge.
4. Write the molecular ion for methane as \(C\_1H\_4^{+}\), indicating the methane molecule with a positive charge due to the loss of one electron.
5. Note that fragment ions such as \(C\_1H\_3^{+}\) or \(C\_1H\_2^{+}\) result from further fragmentation after ionization, but the molecular ion itself retains the full molecular formula with a positive charge.