MCAT Chem/Phys

I missed this question on an official AAMC practice exam or question pack. Teach me why, don't just tell me the answer.

Section: [C/P / CARS / B/B / P/S]
The question, with all answer choices (and the passage or figure if there is one): [PASTE QUESTION]
My answer: [MY ANSWER]. Correct answer: [CORRECT ANSWER].
Why I picked mine: [ONE LINE]

Please:
1. Explain why the correct answer is right. For science passages, separate what the passage or figure says from the outside content needed. For CARS, quote the passage words that prove the answer; no outside knowledge.
2. Pinpoint the mistake in my reasoning and label it: didn't know the content / wrong method / misread / careless / timing.
3. Give me a one-line rule to use next time.
4. If this was a CARS question, don't write new practice questions; name the question type, give me 3 things to check in the answer choices next time, and point me to official AAMC CARS practice. Otherwise, write 2 similar practice questions (not official) with answers and short explanations. Before you show them, silently solve each one again from scratch. If your two solutions disagree, or more than one choice could be right, rewrite or drop that question. Show only the final, clean questions, not your checking.

Trust the official answer key. If it looks wrong to you, say so, but assume I made a typo first and ask me to check.