Why electron flows in the opposite side of electric field

Question

I am facing form this problem that why the electron flow in the opposite side of the electric field

Answer 1

The direction of the electric field is not defined or observed in nature - it is a matter of convention. When the concept of the electric field was introduced by Faraday and formalised by Maxwell in the $19$th century, the existence of the electron was not known, so a conventional direction for the field was picked arbitrarily.

When the electron was discovered by J.J. Thomson in $1896$ in cathode rays, it was found that it moved in the opposite direction to the conventional electric field. Instead of re-defining the electric field direction (which would have meant re-writing hundreds of textbooks and papers and caused endless confusion), it was simpler to define the charge on the electron as negative.

Of course, this means that the proton (which can also be a charge carrier in anode rays, for example) has a positive charge and moves in the same direction as the electric field.