what is meant by oxidation and reduction and what are the differences between them?Though there is oxidation number why there is no number to represent reduction?
This is certainly how we MODEL oxidation and reduction, but I wonder if the way it manifests experimentally is just more of a series of patterns in reactivaty that we describe in terms of "oxidation state" and whatnot. Partial charge, after all, is not an experimental observable. I have heard of people trying to use EXAFS or some such thing to gauge the charge density around certain nuclei in certain environments, but that's not really the same thing.this is a very good question.
oxidation and reduction describe the loss or gain, respectively, in the number of electrons. For example Li+ ion can be reduced to Li0 (also known as elemental or lithium metal) if one electron is added to it. Similarly, S2- ion can be oxidized to S0 (elemental sulfur) ion by removing two electrons. If multiple covalent bonds exist between atoms (common in organic compounds), reduction manifests in the decrease in the number of bonds. A double bond will be reduced to a single bond (due to a gain in the overall number of electrons by addition of hydrogen).
the reason the oxidation state of an atom is monitored in a compound is simply convention. the reduction state could be monitored as well, in principle.
most chemical reactions involve a gain or loss of electrons.