Hint: You can find the number of valence electrons in an atom if you know its atomic number or electronic configuration. Atomic number of potassium is 19. By filling out the shells present in the atom in sequential order we can find out the valence electrons.
Complete Step by step answer: Potassium is an element present in the very first group of the periodic table. It decides the valency which is the most important number as it provides ground for the most of the properties of the elements. We know that the atomic number of Potassium is 19. Its electronic configuration will be 2,8,8,1. So this implies that the outermost shell is having one electron so this implies that valence of Potassium will be 1.
So the correct option is 2nd.
Additional Information: In periodic table, The Group 1 atoms have 1 valence electron. The Group 2 atoms have 2 valence electrons. The Group 3 atoms have 3 valence electrons. The Group 4 atoms have 4 valence electrons. And so on we can find the no. of valence electrons. Valence electrons are the most important thing in chemistry as it decides the most of the chemical properties of the elements.
Note: Valence is the combining power of an element. Elements in the same group of the periodic table have the same valence. The valence of an element is related to how many electrons are in the outer shell.