Emf of the cell, `E_(1)=1.25 V`
Balance point of the potentiometer, `l_(1)=35` cm
The cell is replaced by another cell of emf `E_(2)`
New balance point of the potentiometer, `I_(2)=63` cm
The balance condition is given by the relation,
`(E_(1))/(E_(2))=(I_(1))/(I_(2))`
`E_(2)=E_(1)xx(l_(2))/(l_(1))`
`= 1.25 xx (63)/(35) = 2.25 V`
Therefore, emf of the second cell is 2.25 V.