Element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following

(A) Mg

(B) Na

(C) P

(D) Ca



Let’s go through the options:


  • Mg is highly reactive and relatively soft
  • It only reacts with air to form a protective oxide layer.
  • It does not react with cold water


  • Na is the most reactive metal in the reactivity series  
  • It reacts vigorously with water .
  • It is also very soft and can be cut with a knife.


  • P is a highly reactive element and it is soft.
  • It reacts vigorously with air and cannot be exposed to it without igniting
  • It does not react with water .
  • It is stored inside water to prevent exposure to air. 


  • Ca is a highly reactive metal
  • It is relatively soft and can be cut with a knife
  • It reacts with cold water and air to form hydroxides and oxides respectively. 

So, the correct answer is (b) Na

  1. Class 10
  2. Chapter 3 Class 10 - Metals and Non-Metals (Term 1)

About the Author

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo