The correct option is A CH3(CH2)15N+(CH3)3Br−
At the critical micelle concentration, the anions are pulled into the bulk of the solution and aggregate to form a spherical shape.
Longer the hydrophobic part of the molecule, the micelle formation will be easier. Since, the hydrophobic part is longer in CH3(CH2)15N+(CH3)3Br−, it forms micelles in an aqueous solution at the lowest molar concentration at the ambient condition.