Potassium is kept in the s-block
of the periodic table. Why?

Potassium is an s block element as the electrons of potassium are in the outermost s orbital in an electron shell. EXPLANATION: Alkali metals are known to be group 1 metals placed in s block.

Because Pottasium's last electron enters in the s orbital of its last shell.

Explanation:

In electron configuration, the elements in which the last electron enters in the last s orbital are included in s block. The group 1 and 2 are in this block.