[Hubert]

can some one explain the meaning of reduction in greater details to me...i still dun reallu understand

[movies]

A reduction is when a molecule undergoes a reaction in which it gains electrons.  In organic chemistry, the most common form of this is a ketone reduction by a hydride donor like NaBH₄ or LiAlH₄.  In these reactions, the electrons come in the form of a net H^- delivery.  Another common reduction reaction is hydrogenation of alkenes by H₂ with a heterogeneous catalyst like Pd/C.  In this case, the electrons that are delivered likely come from the H-H bond (the mechanism of this process is not well understood).

In my experience, organic chemists rarely think of reduction in terms of electron delivery and instead opt for a definition that depends more on recognizing different oxidation states.  For example, any experienced organic chemist would recognize that an alcohol and a ketone are related by a difference in oxidation state.  That is to say, a alcohol can be formed by reduction of a ketone and a ketone can be formed by oxidation of an alcohol.  There are five principle oxidation states of carbon: the alkane state (e.g. methane), the alcohol state (e.g. methanol), the ketone/aldehyde state (e.g. formaldehyde), the acid/ester state (e.g. formic acid), and the carbon dioxide state (e.g. carbon dioxide).  There are, of course, other members of each of these states.  They are also occassionally referred to by number, with the alkane state being the "zero level" and the CO₂ level being the 4th level.

If you can recognize the oxidation states then you can tell if a particular reaction is an oxidation, reduction, or neither by how the oxidation state of the molecule has changed.

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