To determine which element has atoms with valence electrons in a higher energy level than those of calcium, we need to look at the electron configuration and energy levels of valence electrons for each element:
- Calcium (Ca) has the atomic number 20 with the electron configuration: \( [Ar] 4s^2 \). The valence electrons (2) are in the 4th energy level.
Now, let's analyze the options:
A. Cesium (Cs): Atomic number 55, electron configuration: \( [Xe] 6s^1 \). The valence electron is in the 6th energy level.
B. Lithium (Li): Atomic number 3, electron configuration: \( 1s^2 2s^1 \). The valence electron is in the 2nd energy level.
C. Bromine (Br): Atomic number 35, electron configuration: \( [Ar] 4s^2 3d^{10} 4p^5 \). The valence electrons are in the 4th energy level.
D. Oxygen (O): Atomic number 8, electron configuration: \( 1s^2 2s^2 2p^4 \). The valence electrons are in the 2nd energy level.
From this analysis, only cesium (A) has valence electrons in a higher energy level (6th energy level) than calcium (4th energy level).
The correct answer is A. cesium.
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