MCQ Detailed View

Chalk is a soft, white, porous sedimentary rock commonly used for writing on blackboards and in art. Chemically, the main component of chalk is Calcium Carbonate (CaCO₃). This makes chalk similar to limestone, but chalk is generally softer and easier to grind into powder.

Calcium carbonate is a naturally occurring compound that provides several important properties to chalk. Its white color, fine texture, and ability to write smoothly on surfaces make it ideal for educational and industrial purposes. The chemical formula CaCO₃ indicates that it contains one calcium atom, one carbon atom, and three oxygen atoms.

When chalk reacts with acids, it produces carbon dioxide (CO₂) gas. For example, if you drop hydrochloric acid (HCl) on chalk, it fizzes as CO₂ is released. This reaction demonstrates the chemical properties of calcium carbonate and is often used in classroom experiments to teach about acid-carbonate reactions.

Other options listed in the question are incorrect:

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  Sodium nitrate (NaNO₃) is used in fertilizers and explosives.

  
  


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  Zinc sulfate (ZnSO₄) is used in medicine and agriculture.

  
  


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  Sulphuric acid (H₂SO₄) is a strong acid used in industrial processes.

  
  

Therefore, the correct chemical name of chalk is Calcium Carbonate (Option 4). Understanding this helps students link everyday substances to their chemical composition, a fundamental part of chemistry learning. Chalk’s use in schools, art, and even construction emphasizes the practical importance of CaCO₃ in daily life.