b
Repulsive force of magnitude \(6 \times 10^{-3} \,N\)

Charge on the first sphere, \(q_{1}=2 \times 10^{-7} \,C\)

Charge on the second sphere, \(q_{2}=3 \times 10^{-7} \,C\)

Distance between the spheres, \(r=30 \,cm =0.3\, m\)

Electrostatic force between the spheres is given by the relation

\(F=\frac{1}{4 \pi \varepsilon_{0}} \cdot \frac{q_{1} q_{2}}{r^{2}}\)

Where, \(\varepsilon_{0}=\) Permittivity of free space and \(\frac{1}{4 \pi \varepsilon_{0}}=9 \times 10^{9} \,Nm ^{2} \,C ^{-2}\)

Therefore, force

\(F =\frac{9 \times 10^{9} \times 2 \times 10^{-7}}{(0.3)^{2}}=6 \times 10^{-3} \,N\)

Hence, force between the two small charged spheres is \(6 \times 10^{-3}\; N\). The charges are of same nature. Hence, force between them will be repulsive.