Question 25 - MCQs from NCERT Exemplar - Chapter 3 Class 10 - Metals and Non-Metals

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

Answer.:

Let’s go through the options:

Mg:

• 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:

• 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:

• 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.: 

• 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