Question

what is reduction ...​

Answer 1

The removal of Oxygen and the addition in a compound of Hydrogen is called reduction.

In the language of Chemistry.....

Hope it helps....

Answer 2

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What is Reduction Reaction ?

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$\textbf{Reduction :}$ The chemical reaction in which oxygen is removed from the compound and hydrogen is added is known as the reaction of Reduction.
In reduction Gain of electrons occurs.

Example :

$CuO + H_{2} \xrightarrow{heat} Cu + H_{2}O$

Here, CuO ( Copper Oxide ) reacts with $H_{2}$ ( Hydrogen gas )
to form Cu (oxygen is removed) and $H_{2}O$ ( Hydrogen is added ).