Final answer:
In the electron configuration for Helium, 1s², the '1' indicates the first energy level, which is the shell closest to the nucleus with the lowest-energy electrons.
Step-by-step explanation:
In the electron configuration for Helium, 1s², the '1' represents the energy level at which the electrons reside. This energy level is the closest to the nucleus and has the lowest energy compared to higher energy levels. The number 1 denotes that the electrons are in the first shell, which is the most stable and lowest energy level available in Helium. There is only one subshell in the first shell, termed as 's', and it can hold a maximum of two electrons. Hence, the complete notation of 1s² accurately describes Helium's electron configuration with both electrons in the first energy level, filling up the single s subshell.