What is oxidation number? Md. Saifur Rahman The number of electrons lost to form a positive ion or the number of electrons gained to form negative ion by an element while forming a compound is called the oxidation number of that element. You may likeDo I need car insurance?What is car insurance?How could I get cheaper car insurance?What is auto insurance?Why Adulterant food is the barrier to sound health?What are the producers?What are food preservatives?What is food chain?What is tertiary consumer?