Final answer:
Aluminum is an atom with a single unpaired electron in its valence shell, with a configuration of 3s²3p¹. So the correct option is A.
Step-by-step explanation:
The atom in the ground state that has only one unpaired electron in its valence shell among the given options is aluminum (Al). Aluminum has the valence electron configuration of 3s²3p¹, which means that two electrons in the 3s orbital are paired and one electron in the 3p orbital is unpaired. This gives aluminum a total of three valence electrons, with just one unpaired electron, which is depicted with three dots around the symbol for aluminum; two of these dots are paired to represent the 3s electrons, and one is unpaired to represent the 3p electron.