In a technical database for a signal processing firm, a data entry clerk must categorize inputs according to their mathematical properties. If a value has a real part of zero ($a = 0$) in the form $a + bi$, it is classified as a pure imaginary number. Which of the following entries should be marked as a pure imaginary number?

A quality control technician is auditing the outputs of an electronic sensor. The outputs are recorded as complex numbers in the standard form $a + bi$. To categorize an output as a pure imaginary number, the value of the real part $a$ must be exactly ____.

A technical manual for a data analysis tool states that a complex number in the standard form $a + bi$ is classified as a pure imaginary number if the real part $a$ is equal to zero.

A laboratory technician is configuring a data-logging tool to categorize complex number readings for a technical report. Arrange the logical steps the tool must follow to correctly identify and represent a pure imaginary number, starting from the general standard form $a + bi$.

Technical Standards for Signal Processing