Cell potential becomes zero when the concentration of the acid increases and it result in battery stratification.
Option: c
Step-by-step explanation:
This happens because sulfuric acid in ‘electrolyte mixture’ divides from the water and begins to concentrate at the bottom of the battery. So increase concentration of acid increases the formation of lead sulfate i.e sulfation took place and gets discharged. Hence immediately needed to be charged to avoid hard crystals which lead sulfate start forming and then it cannot be reconverted.