The correct set of four quantum numbers for outermost electron of potassium (Z=19) is

Electronic configuration of potassium, K (Z =19) is (Ar)184s1. Thus, the outermost configuration is 4s1=4,l=0,m=0,s=1/2 because for n=4,l=0 to n−l i.e., 0 to 3;m=−l to 0 to +l, for l=0,m=0;s=+12 or −12.So,the correct answer is (b).