A substitution reaction is a type of chemical reaction in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms. In Hindi, it is known as "प्रतिस्थापन अभिक्रिया". Here is an example of a substitution reaction in Hindi:

एक उदाहरण है कि जब ब्रोमीन (Br2) को एथेन (C2H4) के साथ विस्फोट कराया जाता है, तो ब्रोमोएथेन (C2H4Br2) बनता है। इसमें ब्रोमीन के दो अणु एथेन के दो अणु के स्थान पर प्रतिस्थापित हो जाते हैं।

Translation: An example is when bromine (Br2) is reacted with ethene (C2H4), then dibromoethene (C2H4Br2) is formed. In this, the two atoms of bromine are substituted for the two atoms of ethene.