b
\( L.C.=\frac{P}{N}=\frac{0.5\,mm}{50}=0.01\,mm\)

Length of wire \(=6.8 cm\)

Diameter of wire \(=1.5\,mm +7 \times L.C\)

\(=1.5\, mm +7 \times .01=1.57\,mm\)

Curved surface area \(=\pi Dl\)

\(=3.14 \times 6.8 \times 1.57 \times 10^{-1} cm^{2}\)

\(=3.352\,cm ^{2}=3.4\,cm ^{2}\)