Final answer:
The reduction signify in organic chemistry is gain of one or more electrons in a chemical reaction
Step-by-step explanation:
The substance that gains electrons is said to be reduced. Reduction can be defined in terms of changes in composition or in terms of the gain or loss of hydrogen atoms.
For example, if a molecule gains oxygen atoms or loses hydrogen atoms, it is being reduced. Conversely, if a molecule loses oxygen atoms or gains hydrogen atoms, it is being oxidized. It is important to note that oxidation and reduction always occur together in a chemical reaction.
In the conversion of acetaldehyde into ethanol, acetaldehyde gains hydrogen atoms, so it is being reduced. Therefore in organic chemistry, reduction refers to the gain of electrons in a chemical reaction. It can be defined in terms of changes in composition or the gain or loss of hydrogen atoms.