Answer:
A. 6 or D. 8
Step-by-step explanation:
The equivalent emf of n number of cells in series combination is the sum of their individual emfs.
In the first case, if we connect six 2V cells in series, it would give 12V. On the other hand, if we connect eight 1.5V cells in series, it would also give 12 V. Assuming in both cases that the cells have negligible internal resistance.
The number of cells to be connected in series depends on the emf of the cells and the total emf required.