In the following figure a wire bent in the form of a regular polygon of n sides is inscribed in a circle of radius\[a\]. Net magnetic field at centre will be

• A. \[\frac{{{\mu }_{0}}i}{2\pi a}\tan \frac{\pi }{n}\]                       
• B. \[\frac{{{\mu }_{0}}ni}{2\pi a}\tan \frac{\pi }{n}\]
• C. \[\frac{2}{\pi }\frac{ni}{a}{{\mu }_{0}}\tan \frac{\pi }{n}\]        
• D. \[\frac{ni}{2a}{{\mu }_{0}}\tan \frac{\pi }{n}\]