Step 1: Define the Potential Relation for a Sphere
The electric potential on a sphere is given by:
\[
V = \frac{Q}{R}
\]
When 125 spheres merge, the total charge increases by a factor of 125, while the radius increases by a factor of:
\[
R_{\text{new}} = R_{\text{old}} \times 125^{1/3} = 5 R
\]
Step 2: Compute the New Potential
Since \( V \propto \frac{Q}{R} \), the new potential is:
\[
V_{\text{new}} = \frac{60 \text{ mV} \times 125}{5} = 1.5 \text{ V}
\]