Final answer:
The orbital notation for an s-block element in the third period is B. 2s² 2p⁶ 3s², showing the electron configuration of sodium (Na) with a filled 2p subshell and two electrons in the 3s subshell.
Step-by-step explanation:
The question asks which orbital notation represents an s-block element in the third period. The third period starts filling the 3s subshell, and the s-block elements have their outermost electrons in an s orbital. The correct notation for an s-block element in the third period would be the one where the 3s subshell is being filled but not completed, or is filled and no electrons are in higher energy levels.
From the options, the correct answer is B. 2s² 2p⁶ 3s². This represents sodium (Na), which has its outermost electrons in the 3s orbital, and is an s-block element of the third period. The electron configuration shows a filled 1s and 2s subshell, a filled 2p subshell, and two electrons in the 3s subshell, indicating its position in the s-block.