A metal wire of linear mass density of $9.8 \mathrm{~g/m}$ is stretched with a tension of 10 kg-wt between two rigid supports 1 metre apart. The wire passes at its middle point between the poles of a permanent magnet, and it vibrates in resonance when carrying an alternating current of frequency $n$. The frequency $n$ of the alternating source is\\
(1) 50 Hz\\
(2) 100 Hz\\
(3) 200 Hz\\
(4) 25 Hz