Final answer:
Astatine (At) aims to achieve the electron configuration of radon (Rn) by gaining one electron, thus reaching the stable noble gas configuration.
Step-by-step explanation:
The noble gas that astatine (At) wants to be like is the noble gas closest to it in the periodic table, which is radon (Rn). Atoms often gain, lose, or share electrons to achieve the same number of electrons as the noble gas closest to them in the periodic table, a state known as a noble gas configuration, which is associated with maximum stability.
Astatine, being one halogen away from the noble gases, would tend to gain one electron to achieve the electron configuration of radon. This provides astatine with a full valence shell, mimicking the electron configuration of a noble gas.