c
\(\text { Here, } v_{\text {air }}=350 \mathrm{m} / \mathrm{s}, v_{\text {brass }}=3500 \mathrm{m} / \mathrm{s}\)

When a sound wave travels from one medium to another medium its frequency remains the same

\(\because \quad\) Frequency, \(v=\frac{v}{\lambda}\)

since \(v\) remains the same in both the medium

\(\Rightarrow \quad \frac{v_{\text {air }}}{\lambda_{\text {air }}}=\frac{\nu_{\text {brass }}}{\lambda_{\text {brass }}}\)

\(\lambda_{\text {brass }}=\lambda_{\text {air }} \times \frac{V_{\text {brass }}}{V_{\text {air }}}=\lambda_{\text {air }} \times \frac{3500}{350}=10 \lambda_{\text {air }}\)