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A magnet of magnetic moment M oscillating freely in earth's horizontal magnetic field makes n oscillations per minute. If the magnetic moment is quadrupled and the earth's field is doubled, the number of oscillations made per minute would be

(a) $\frac{n}{2\sqrt{2}}$                         (b) $\frac{n}{\sqrt{2}}$

(c) $2\sqrt{2}n$                        (d) $\sqrt{2}n$