c
\(\text { Here, } B=3.57 \times 10^{-2}\, \mathrm{T}\)

\(\frac{e}{m}=1.76 \times 10^{11}\, \mathrm{C\,kg}^{-1}\)

Frequency of revolution of the electron,

\(v=\frac{1}{T}=\frac{v}{2 \pi r}.........(i)\)

Also, \(\frac{m v^{2}}{r}=e v B \Rightarrow \frac{v}{r}=\frac{e B}{m}.........(ii)\)

From eqns. \((i)\) and \((ii)\),

\(v=\frac{1}{2 \pi} \times \frac{e B}{m}=\frac{1}{2 \times 3.14} \times 1.76 \times 10^{11} \times 3.57 \times 10^{-2}\)

\(=10^{9} \,\mathrm{Hz}=1 \,\mathrm{GHz}\)