Which of the following is the most reactive metal?  

Potassium 

The correct answer is option 2. Potassium.

Among the options provided, potassium is the most reactive metal.

Potassium belongs to Group 1 of the periodic table, also known as the alkali metals. Alkali metals are highly reactive due to their low ionization energies, which makes them readily lose electrons to form positively charged ions. Among the alkali metals, potassium is more reactive than sodium due to its lower ionization energy, making it more prone to react vigorously with water and other substances.

So, the correct answer is: Potassium