Answer
(c) eight
Work Step by Step
As the connection is in series,
Overall output voltage= sum of individual voltages
Batteries are identical. Therefore
Overall output voltage= n$\times$ voltage of one battery
where n is the number of batteries connected.
$\implies 12\,V=n\times1.5\,V$
Or $n=\frac{12\,V}{1.5\,V}=8$
