Answer:
The assertion and reason provided are both correct.
The internal resistance of a cell refers to the opposition to the flow of electric current within the cell itself. The assertion states that the internal resistance of a cell is constant. This is generally true because the internal resistance depends on factors like the size, design, and materials of the cell, which tend to remain relatively constant during normal operation.
The reason provided for the assertion is also correct. The ionic concentration of the electrolyte, which is the solution inside the cell that facilitates the movement of ions, does indeed remain relatively constant during the use of a cell. This is especially true for well-designed and well-maintained cells. The consistency in ionic concentration contributes to the internal resistance remaining relatively constant.
In conclusion, the assertion that the internal resistance of a cell is constant is supported by the reason that the ionic concentration of the electrolyte remains the same during the cell's use.