(b) 3
Let the height of the cylindrical iron rod be h cm. Then,
Radius of iron rod = Radius of spherical ball = \(\frac{h}{4}\) cm.
∴ Number of spherical balls = \(\frac{\text{Volume of cylindrical rod}}{\text{Volume of spherical ball}}\)
= \(\frac{π\times\big(\frac{h}{4}\big)^2\times{h}}{\frac43\timesπ\times\big(\frac{h}{4}\big)^3}=3.\)