Final answer:
The element with a valence configuration of 2s1 is Lithium (Li). However, lithium (Li) has the electron configuration 1s²2s¹, which matches the given valence configuration of 2s1.
Step-by-step explanation:
The element that has a valence configuration of 2s1 is Lithium (Li).
The alkali metals such as Na, K, Rb, and Cs have a single valence electron in the s-orbital of their outermost energy level.
For example, sodium (Na) has the valence configuration [Ne]3s¹.
However, lithium (Li) has the electron configuration 1s²2s¹, which matches the given valence configuration of 2s1.