The correct answer is K. 

 Key Points

• The chemical symbol for potassium is K.
• Potassium is a chemical element with the symbol K and atomic number 19.
• Classified as an alkali metal, potassium is a solid at room temperature.
• The word potassium is derived from the substance potash.
• The element has been in use for hundreds of years.
• It is an alkali metal along with lithium, rubidium, sodium, caesium, and francium.
• It is a very reactive metal and is never found free in nature, always forming a compound with other elements.
• Potassium typically has three isotopes, known as potassium-39, 40, and 41.
• Potassium-40 is highly radioactive and can be found in rocks, plants, and animals.
• It is used to measure the age of objects.

 Additional Information