Which of the following contain + M but - I effect - A) O = CH –
B) – NO2
C) –Cl
D) CH3-

Oxidation
oxidation is a process in oxygen is added to a substace . e.g.
1 : - 4na + o₂ > > > > 2na₂o
2: -   2h₂ + o₂> > > >   2h₂o
 
reduction
reduction is the process in oxygen is removed from a substance . eg.
  1  : -   cuo+h₂> > > > cu+h₂o
  2: -   2pbo+c> > > > >   pb+co₂

redox
redox is a combination if oxidation and reactions involves  transfer of electrons between two species. e.g.
1: -  2fe³⁺   + sn2+===> > >   2fe²⁺  + sn⁴⁺
2: -  fe + cu²⁺   > > >   fe²⁺   + cu