Which of the following represents pure capacitive reactance of 100 ohms in rectangular notation?

In rectangular notation, impedance is expressed as R + jX, where R represents resistance (the real part) and X represents reactance (the imaginary part). Because the question specifies 'pure' capacitive reactance, there is zero resistance, meaning R = 0. By mathematical convention in electronics, inductive reactance is represented as a positive imaginary number (+j) and capacitive reactance is represented as a negative imaginary number (-j). Therefore, 100 ohms of capacitive reactance is written as -j100. Combining these facts, pure capacitive reactance of 100 ohms is perfectly represented as 0 - j100. An option like '0 + j100' would represent pure inductive reactance.