Question

Assertion: Sodium reacts vigorously with cold water but magnesium does not react with cold water.
Reason: Sodium is more reactive than magnesium.

• A. Assertion: True, Reason: False
  
  Reason is not the correct explanation of assertion.
• B. Assertion: True, Reason: True
  
  Reason is the correct explanation of assertion.
• C. Assertion: False, Reason: False
• D. Assertion: False, Reason: True

Answer 1

The correct option is B Assertion: True, Reason: True


Reason is the correct explanation of assertion.

Sodium reacts vigorously with water and produces sodium hydroxide and hydrogen gas. The hydrogen gas evolved immediately catches fire as the reaction is highly exotermic.
The reaction involved is:

${\text{2Na(s) + 2H}}_2\text{O(l)}\to {\text{2NaOH(aq) + H}}_2\text{(g)}$

On the other hand, magnesium does not react with cold water and hot water. It reacts only with steam. The reaction involved is:

${\text{2Mg(s) + 2H}}_2\text{O(g)}\to {\text{2MgO(s) + H}}_2\text{(g)}$

This proves sodium is much more reactive than magnesium.