tan 5° tan 25° tan 30° tan 65° tan 85° = ?

$\tan 5^{\circ} \tan 25^{\circ} \tan 30^{\circ} \tan 65^{\circ} \tan 85^{\circ}$

$=\tan \left(90^{\circ}-85^{\circ}\right) \tan 25^{\circ} \tan 30^{\circ} \tan \left(90^{\circ}-25^{\circ}\right) \tan 85^{\circ}$

$=\cot 85^{\circ} \tan 25^{\circ} \tan 30^{\circ} \cot 25^{\circ} \tan 85^{\circ} \quad\left(\because \tan \left(90^{\circ}-\theta\right)=\cot \theta\right)$

$=\left(\frac{1}{\tan 85^{\circ}} \tan 85^{\circ}\right)\left(\tan 25^{\circ} \frac{1}{\tan 25^{\circ}}\right) \tan 30^{\circ} \quad\left(\because \cot \theta=\frac{1}{\tan \theta}\right)$

$=\tan 30^{\circ}$

$=\frac{1}{\sqrt{3}}$

Hence, the correct option is (c).