The correct option is C 125%
Let original side be L units in length.
New side length = 1.5L (after increase).
Original surface area = 6×L2
Increased surface area = 6×(1.5L)2=13.5L2
Then, % increase in surface area
=Increased surface area−Original surface areaOriginal surface area×100
=13.5L2−6L26L2×100=125%
[Alternate method:
Let the edge be a cm.
New edge (after increase)
=a+50%a=a+a2=3a2
TSA of the original cube =6a2
TSA of new cube
=6×(3a2)2=6×9a24=2.25×6a2
Increase in area =[2.25×6a2]−[6a2]=(2.25−1)×6a2=1.25×6a2=1.25×TSA of the original cube
⇒ Increase %=125%]