Answer:
C. Alkali metals
Step-by-step explanation:
The three main groups of elements are metals, nonmetals, and alkali metals, also known as group 1 elements. Alkali metals are a subset of metals that include elements such as lithium, sodium, and potassium. They are called "alkali" because they react with water to form alkaline (basic) solutions. Alkali metals are highly reactive, soft, and have low melting points. They have one electron in their outermost shell, which makes them very reactive and prone to forming ions with a positive charge. These elements are found in nature only in compounds and not as pure elements.