The correct answer is Potassium.

Key Points

• Potassium (K) is the most reactive metal and reacts vigorously with air and water.
  • A large amount of heat is generated during their reaction.
  • To avoid such accidents, this metal is kept immersed in kerosene oil.
  • Potassium reacts with water in a similar way to sodium; the products of the reaction are potassium hydroxide and hydrogen gas.
  • This reaction releases a large amount of heat energy, which often ignites the hydrogen gas produced.
• Sodium (Na) and lithium (Li) are also highly reactive to air and water and need to be stored under oil to prevent them from reacting with gases in the air and water.
• Cesium (Cs) is the most reactive of all metals.

Additional Information

• Metals react with water and oxygen present in the air.
• Metals with high reactivity have faster reactions.
• For example, sodium catches fire in the air, which is why it is kept in kerosene oil.
• Due to such reactivity of metals, most metals are not available in a free state in nature.
• They exist in the form of their compounds (oxides, carbonates, sulfides, etc.).
• Some metals that are least reactive are available in a free state.
• Such metals are gold, silver, platinum.