To find the number of unpaired electrons in copper (Cu), we need to write down its electron configuration. The atomic number of copper is 29 , indicating it has 29 electrons. Copper, a transition metal, can sometimes have an electron configuration that is an exception to the typical filling order due to the relative energies of the atomic orbitals. The generally expected electron configuration would follow Hund's rule and the Aufbau principle, filling orbitals from lowest to highest energy level. However, copper exhibits a unique electron arrangement where one electron in the 4 s orbital is used to complete the 3d subshell, resulting in a more stable configuration. Its electron configuration in the ground state is: Cu: [Ar]3d104s1 When we look at this configuration: The 3d subshell is completely filled with 10 electrons, which means all five 3d orbitals have paired electrons. There are no unpaired electrons in the 3d subshell. The 4 s subshell has 1 electron. This means there is just one unpaired electron in the 4 s orbital. Therefore, in its ground state, copper has a total of 1 unpaired electron. The answer to the question is: Option A: 1