A bead of mass m is attached to one end of a spring of natural length R and spring constant\[k=\frac{(\sqrt{3}+1)mg}{R}\] The other end of the spring is fixed at a point A on a smooth vertical ring of radius R as shown in the figure. The normal reaction at B just after it is released to move is

• A. \[mg/2\]           
• B. \[\sqrt{3\,}mg\]
• C. \[3\sqrt{3\,}mg\]           
• D. \[\frac{3\sqrt{3}mg}{2}\]