M+1 Peak from 13C Isotope Abundance Steps:

• Vitamin C (C₆H₈O₆) has 6 carbon atoms; molecular ion M⁺ at m/z 176 has 7.0% relative abundance.
• M+1 peak at m/z 177 arises mainly from one ¹³C replacing ¹²C; ¹³C natural abundance is 1.1%.
• Relative intensity of M+1 to M is 6 × (1.1 / 100) = 0.066.
• M+1 abundance = 0.066 × 7.0% = 0.462%, which rounds to 0.48%.

Why A is correct:

• Matches calculation using formula for ¹³C contribution: (number of C atoms × ¹³C abundance / 100) × M abundance.

Why the others are wrong:

• B: Assumes ~1.4% ¹³C abundance (too high).
• C: Assumes ~1.46% ¹³C abundance (too high).
• D: Assumes ~2.1% ¹³C abundance (too high).

Final answer: A