a
Given : Magnetic moment, \(M=6.7 \times 10^{-2}\, \mathrm{Am}^{2}\)

Magnetic field, \(\mathrm{B}=0.01\, \mathrm{T}\)

Moment of inertia, \(I=7.5 \times 10^{-6}\, \mathrm{Kgm}^{2}\)

\(\text { Using, } T =2 \pi \sqrt{\frac{I}{M B}} \)

\(=2 \pi \sqrt{\frac{7.5 \times 10^{-6}}{6.7 \times 10^{-2} \times 0.01}}=\frac{2 \pi}{10} \times 1.06\, s\)

Time taken for \(10\) complete oscillations

\(t=10\, T=2 \pi \times 1.06 \)

\(=6.6568 \approx 6.65\, \mathrm{s}\)