Why does the s-block portion of the periodic table span two groups?

There are two groups in the s-block because these elements have only the s orbital filling the outer electron shell. Group 1 are elements that only have 1 electron in the s orbital. Group 2 are elements that have 2 electrons in the s orbital.

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.

Outermost (valence) electrons