Question

When an element 'X' reacts with water, it starts floating. Identify the element 'X':

• A. Potassium
• B. Calcium
• C. Sodium
• D. Iron

Hint:

Reaction of metals with water:

• K, Na: Violent, float (low density), catches fire
• Ca: Less violent, floats due to H₂ bubbles
• Mg: Reacts with hot water
• Fe, Al: React with steam

Answer 1

The Correct Option is B

To identify the element 'X' that reacts with water and starts floating, we need to understand the behavior of the given options (Potassium, Calcium, Sodium, and Iron) when they react with water.

1. Potassium: Potassium reacts vigorously with water and produces hydrogen gas. However, it does not float because potassium is denser than water initially.
2. Calcium: When calcium reacts with water, it forms calcium hydroxide and hydrogen gas. The release of hydrogen gas causes calcium to start floating. This is because the bubbles of hydrogen gas get trapped on the surface of the calcium, making it less dense.
3. Sodium: Sodium reacts vigorously with water like potassium and also produces hydrogen gas. Sodium does not float initially due to its density.
4. Iron: Iron does not react directly with water under normal conditions and does not float on water.

Based on this analysis, Calcium is the correct answer because it reacts with water and starts to float due to the production of hydrogen gas bubbles.