what is voltage drop in an electric circuit ?. is voltage drop essential in electric circuit.  what would happen if  there would be no voltage drop

When a cell is in open circuit, the potential difference between the terminals of the cell is called emf (e).

When a cell is in closed circuit, the potential difference between the electrodes of the cell is called terminal voltage (V).

In closed circuit, the terminal voltage (V) is always less than the emf (e) by the amount of energy spent in the flow of unit positive charge through the electrolyte of the cell. If w is the work done (or energy spent) in carrying a test charge q_o through the electrolyte of the cell, then the quantity (w/q_o) is called the voltage drop (v).

i.e., v = w/q_o

Definition: The work done in carrying a unit positive charge through the electrolyte is called the voltage drop in the cell.

It is so called because this voltage is not available to us for use.

Yes, a voltage drop is essential in electric circuit.

No voltage drop would mean no waste of energy, which is practically not possible.