c
\(R _{\text {initial }}=\frac{\rho \ell}{ A }=5 \Omega\)

\(\because\) Volume of wire is constant in stretching

\(V _{ i }= V _{ f }\)

\(A _{ i } \ell_{ i }= A _{ f } \ell_{ f }\)

\(A \ell= A ^{\prime}(5 \ell)\)

\(A ^{\prime}=\frac{ A }{5}\)

\(R _{ f }=\frac{\rho \ell_{ f }}{ A _{ f }}=\frac{\rho(5 \ell)}{\left(\frac{ A }{5}\right)}\)

\(=25\left(\frac{\rho \ell}{A}\right)\)

\(=25 \times 5=125 \Omega\)