Concept:
Alkali metals belong to Group 1 of the periodic table.
They are:
\[
\text{Li},\ \text{Na},\ \text{K},\ \text{Rb},\ \text{Cs},\ \text{Fr}
\]
Step 1: Check the given elements.
• Lithium is an alkali metal.
• Potassium is an alkali metal.
• Caesium is an alkali metal.
• Beryllium belongs to Group 2, so it is an alkaline earth metal.
Hence, the correct answer is:
\[
\boxed{(C)\ \text{Beryllium}}
\]