An element with atomic number 20 is placed in which period of the periodic table?
Correct answer: A. 4
- A. 4
- B. 3
- C. 2
- D. 1
Explanation
The element with atomic number 20 is calcium. Its electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2, indicating it occupies the 4th period. Therefore, Option A is correct. Options B, C, and D are incorrect, as they refer to periods with incomplete shells that do not match calcium's configuration.
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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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