The first ionization energy of Mg is lower than
Correct answer: C. Be
- A. Na
- B. Ca
- C. Be
- D. Al.
Explanation
The first ionization energy generally increases across a period and decreases down a group. Magnesium (Mg) has a lower first ionization energy than Beryllium (Be) because Mg is located to the right of Be in the periodic table, meaning Mg has a larger atomic size and its valence electron is further from the nucleus. In contrast, Be has a smaller atomic size, and its valence electrons are held more tightly, resulting in a higher ionization energy. Sodium (Na) has a lower ionization energy than Mg because Na is to the left of Mg in the same period. Calcium (Ca) has a lower ionization energy because it is below Mg in the same group, where atomic size and shielding increase. Although Aluminum (Al) is to the right of Mg, it has a slightly lower ionization energy than Mg due to a new sublevel being filled, but it is not the correct answer in this context where a clear higher ionization energy example is required.
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About Periodic Properties and Trends
Periodic properties arise from electron configuration and effective nuclear charge, producing trends in atomic and ionic radius, ionization energy, electron affinity, electronegativity, metallic character and reactivity. Comparisons run across periods and down groups, with attention to common exceptions. The topic also relates these trends to the behavior of s-block and p-block elements.
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