Which is not different between primary and secondary cells?
A. reversibility of chemical reaction
B. rechargeability of cell
C. supply of energy to external circuit
D. strength of current

Hint: Both the primary and secondary cell are doing the function of supplying energy to the external circuit. So it is the option which is not different in between the primary and the secondary cell.

Complete step by step answer:
Cell is the energy source in which energy is being produced by chemical reactions and stores it in the form of electric current.

Now let us talk about primary cells and secondary cells. Primary cells are the cell which is single time usable. After that it needs to be disposed of. Primary cells contain electrolytes that are absorbent in nature. That means electrolytes will not be in liquid nature. Therefore they are commonly called as dry cells. Secondary cells are more user friendly so that they can be used further after first discharge. It can be recharged to attain its pre-discharged condition by passing electric current through the circuit in the exact opposite direction. These kinds of cells are nowadays used more commonly.

Both primary and secondary cells complete the purpose of supplying energy to external circuits. The reversibility of chemical reactions as well as the rechargeability of the cells can be possible only in secondary cells. Strength of current is low in primary cells so that they are replaced nowadays by secondary cells whose current strength can be high or low.

Note:
The basic need of any cell is to act like an electrical energy source. Both primary and secondary cells complete the purpose of supplying energy to external circuits. Both primary and secondary cells complete the purpose of supplying energy to external circuits. The reversibility of chemical reactions as well as the rechargeability of the cells can be possible only in secondary cells.