A small coil of N turns has an effective area A and carries a current I. It is suspended in a horizontal magnetic field \[\overrightarrow{B}\] such that its plane is perpendicular to \[\overrightarrow{B}\]. The work done in rotating it by \[180{}^\circ \] about the vertical axis is [MP PMT 1994]

• A.            NAIB                                        
• B.            2NAIB
• C.            \[2\pi NAIB\]                       
• D.            \[4\pi NAIB\]