The set of numbers used to describe the position and energy of the electron in an atom are called quantum numbers. There are four quantum numbers, namely, principal, azimuthal, magnetic and spin quantum numbers.
Electronic configuration of K is:
K=Atomicnumber=191s22s22p63s23p64s1
The outermost electron is in 4s1
∴ n=4,l=0,m=0,s=+21
Hence, the answer is option B.