Question

the internal resistance of a secondary cell is low where as the internal resistance of a primary cell is high . why ??

Answer 1

Primary cells (not chargeable) or Secondary cells (Chargeable) If it is Dry cell, Chargeable cells.If it is new, Internal resistance will be Normal.if it is used or old Internal resistance will increase considerably. Cell Internal temperature also a factor for Internal resistance.If Distilled water added more the Internal resistance will increase. 

The internal resistance of the cell depends upon the size of the electrodes, the distance between them in the electrolyte, and the resistance of the electrolyte. The larger the electrodes and the closer together they are in the electrolyte (without touching), the lower the internal resistance of the cell and the more current the cell is capable of supplying to the load.

Answer 2

It is because the internal parts of a primary cell contains a lot of chemicals which provides resistance to the current.
And secondary cells contain only lead so it provides less resistance as lead is a good conductor of electricity.