Bharat ka mangal par mangalagaman par ek letter hindi main likhiye ,please help me

a chemical reaction  is a process that leads to the transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei  and can often be described by a chemical equation. Nuclear chemistryis a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes may occur.