Given,
Emf of the cell,E1=1.25 V
Balance point of the potentiometer,l1=35 cm
The cell is replaced by another cell of emf E2.
New balance point of the potentiometer,l2=63 cm
The balance condition is given by the relation,
E1E2=l1l2
E2=E1×l2l1
⇒E2=1.25×6335=2.25 V
Therefore, end of the second cell is 2.25 V.