CBSE Class 12-science Answered

Nucleophile means "nucleus loving" which describes the tendency of an electron rich species to be attracted to the positive nuclear charge of an electron poor species, the electrophile .

The nucleophilicity expresses the ability of the nucleophile to react in this fashion.

In general terms this can be appreciated by considering the availability of the electrons in the nucleophile. The more available the electrons, the more nucleophilic the system. 
Hence the first step should be to locate the nucleophilic center.  At this point we will be considering Nu that contain lone pairs and may be anionic, however the high electron density of a  C=C is also a nucleophile. 

Electrophilic means 'electron-loving'. An Electrophile is a chemical species that is electron-deficient. It will seek out an electron-rich site in an organic molecule.

Examples of electrophiles are: H⁺, Cl⁺, Br⁺, I⁺, NO₂⁺, CH₃⁺, CH₃CO⁺, C₆H₅N₂⁺.