How many valence electrons does K have?

Hint: Valence electron can be defined as the electrons present in the outer shell of an atom which can participate in the formation of chemical bond and this combining capacity of any atom is known as valency of that atom.

Complete answer:
K represents the metal known as potassium which have atomic number 19 and this is kept in the category of metals but it have exceptional nature towards metal as all metals are solid in nature but potassium is the only metal that is soft enough to cut with the knife. It is generally a silvery white metal.
Valence electrons can be calculated with the help of electronic configuration of an atom like the electrons present in the outermost shell. To know about this we first have to know the concept of electronic configuration. In this we fill the electrons according to three known rules called Aufbau principle, Pauli Exclusion Principle and Hund’s rule which describes how electrons are filled step by step. Like in s subshell only 2 electrons can be filled, in p subshell at most 6 electrons, d subshell 10 electrons and in f subshell only 14 electrons are present.
The electronic configuration of potassium is given by:
$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{1}}$, Hence the outermost shell i.e. $4s$ contain 1 electron so we can say that the valence electron present in K is one.

Note:
The number of valence electrons in an atom tells us about their bonding behavior. Due to this reason elements whose atoms have the same number of valence electrons are grouped together in the periodic table of the elements.