Which of the following represents a pure inductive reactance in polar coordinates?
Why In polar form an impedance is written as magnitude at an angle, where the angle is set by the ratio of reactance to resistance. A pure inductance has no resistive part, so the impedance lies entirely on the +j axis of the complex plane, giving an angle of +90 degrees. This matches the physical fact that in an inductor the voltage leads the current by a quarter cycle.
Watch out A negative 90 degree angle is pure capacitive reactance, where current leads voltage; 45 degree angles occur only when resistance and reactance are equal in magnitude.
ELI the ICE man: inductor voltage leads, so L sits at +90. Any 45 degree answer means R equals X, not pure reactance.