Q11: Which of the following electron configurations is correct for Cobalt (Co)? A) \( [\operatorname{Ar}] 3 d^{7} 4 s^{2} \) B) \( [\mathrm{Ne}] 4 s^{2} 3 d^{7} \) C) \( [\operatorname{Ar}] 4 s^{1} 4 d^{7} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2} 3 d^{7} \) D) \( [\operatorname{Ar}] 4 s^{2} 3 d^{6} \)

Cobalt (Co), which has an atomic number of 27, has a well-defined electron configuration that reflects its position in the periodic table. It fills the 4s subshell before the 3d subshell, leading to a correct electron configuration of \( [\operatorname{Ar}] 4 s^{2} 3 d^{7} \). This follows the Aufbau principle, which states that electrons occupy the lowest energy orbitals available. In practical terms, understanding electron configurations is vital for predicting how elements behave in chemical reactions. Cobalt, for instance, is known for its catalytic properties and is used in various applications, including batteries and alloys. Recognizing its electron configuration helps in explaining why cobalt is magnetic and has diverse oxidation states, making it essential in chemistry and materials science.