What is "mole" ?

 A mole is the amount of substance that contains as many species [Atoms, molecules ions or other particles] as there are atoms in exactly 12 gm of C-12

                         [1Mole= 6.022x10^23 Species]

What are difference between "Isoelectronic" and "Isosters" species?

Isoelectronic : Ion or atom or molecule or species which have the same number of electron is called Isoelectronic species.

Isosters : Substance which have same number of electron and atoms called Isosters