When the current carrying circular loop of radius R is placed in the x-y plane with center at the origin the magnetic field is along its axis i.e. along z-axis and so is the magnetic moment. So, when one half of the loop is bent then the magnetic moment changes but doesn’t diminish as there will be two equal magnetic moments but perpendicular to each other which will add vectorially to give some non-zero value. But there will be no change in magnitude of B at (0.0.z), z >>R because there is no change in total current in the wire as the formula for B at z>>R is .

Hence, our answer is option(d).