When we say that addition of an electropositive element is reduction then why do we not say that removal of an electropositive element will be oxidation?
Rather we say that removal of an electronegative element will be oxidation but!
If we give it a thought then electropositive and electronegative are two different terms that put innocent  creatures like me in a confusion...!..:p

Dear student
Please find the solution to the asked query:

 Addition of an electropositive element:

  HgCl₂ + Hg* $\to$Hg₂Cl₂  (Reduction of mercuric chloride)

  CuCl₂ + Cu*$\to$ Cu₂Cl₂                      (Reduction of cupric chloride)

The substance which brings reduction is known as reducing agent. The substances marked with asterisk sign (*) in the above equations are reducing agents.

A substance, which undergoes oxidation, acts as a reducing agent while a substance, which undergoes reduction, acts as an oxidizing agent.

Mg, S, Cu, Na₂SO₃, H₂S, HI, H₂, C, KI are reducing agents, while O₂, Cl₂, F₂, H₂O₂, MnO₂, FeCl₃, CuCl₂, Fe₃O₄, CuO, etc., are oxidizing agents in the above examples.

All oxidation and reduction reactions are complimentary of one another and occur simultaneously, one can not take place without the other. No single oxidation and no single reduction process is known. The simultaneously oxidation and reduction reactions are generally termed as redox reactions.

e.g., 2FeCl₃ + SnCl₂ $\to$ 2FeCl₂ + SnCl₄

  2Fe³⁺ + Sn²⁺ $\to$2Fe²⁺ + Sn⁴⁺
 

In above example iron undergoes reduction from +3 to +2 and tin undergoes oxidation from +2 to +4.

Electronegativity is a measure of tendency to attract shared pair of electrons. Non-metals are generally electronegative. 
They readily accepts electron from electropositive or less electronegative atoms. Since losing electrons causes the oxidation, therefore addition of an electronegative atom/element causes oxidation.
Example:
Addition of oxygen(non-metal, electronegative) to zinc having oxidation number = 0 , which changes to +2 in ZnO.
2Zn(s) + O₂(g) $\to$→2ZnO  

 

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