1. The term $6s^2$ refers to an electron configuration notation where $6$ is the principal quantum number (energy level), $s$ is the subshell (orbital type), and $^2$ indicates two electrons occupying that subshell. 2. Writing $6l^2$ is incorrect because $l$ represents the azimuthal quantum number (angular momentum quantum number) which corresponds to subshell types: $l=0$ for $s$, $l=1$ for $p$, $l=2$ for $d$, and $l=3$ for $f$. 3. The letter notation ($s, p, d, f$) is used in electron configurations instead of numbers like $l$ because it clearly indicates the shape and type of subshell. 4. Therefore, you cannot substitute $s$ with $l$, and the correct notation for two electrons in the $s$ subshell of the $6^{th}$ energy level is $6s^2$. Final answer: The term $6s^2$ correctly describes two electrons in the $6s$ orbital, and writing $6l^2$ is incorrect and not used in electron configurations.