MCAT General Chemistry Question 187: Answer and Explanation
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Question: 187
7. The figure below depicts the relative sizes and mole fractions of two monatomic gases in a closed container.
Which of the following is true about the gas mixture after a small hole is punched in the container and the gases are allowed to completely effuse?
- A. Na
- B. K
- C. Mg
- D. Ca
Correct Answer: D
Explanation:
D After their first ionizations, Na+ and K+ both have octet electron configurations, so a second ionization to remove another electron would require a very high amount of energy. This eliminates choices A and B. Ionization energy decreases down a group, due to increased nuclear shielding, so it is easier to remove electrons from Ca than Mg, making choice D the answer.