To determine which element has valence electrons in a higher energy level than calcium, we first need to identify the electron configuration of calcium.
Calcium (Ca) has an atomic number of 20, and its electron configuration is:
\[ \text{Ca: [Ar] 4s}^2 \]
This means that the valence electrons of calcium are in the 4th energy level (the 4s subshell).
Now, let's analyze the options given:
A. Lithium (Li): Atomic number 3. Electron configuration: \[ \text{Li: 1s}^2 , 2s^1 \] (Valence electrons in the 2nd energy level)
B. Cesium (Cs): Atomic number 55. Electron configuration: \[ \text{Cs: [Xe] 6s}^1 \] (Valence electrons in the 6th energy level)
C. Oxygen (O): Atomic number 8. Electron configuration: \[ \text{O: 1s}^2 , 2s^2 , 2p^4 \] (Valence electrons in the 2nd energy level)
D. Bromine (Br): Atomic number 35. Electron configuration: \[ \text{Br: [Ar] 4s}^2 , 3d^{10} , 4p^5 \] (Valence electrons in the 4th energy level)
From this information, we see that cesium (Cs) has valence electrons in the 6th energy level, which is higher than the 4th energy level of calcium.
Therefore, the answer is:
B. Cesium