A rectangular waveform with a duty cycle of exactly 50% (equal high and low times within each period) is more specifically referred to as a:

Introduction:
Different periodic waveforms are classified by shape and timing metrics. Duty cycle is a key descriptor for rectangular waveforms. This question verifies that a 50% duty cycle rectangular wave is called a square wave.

Given Data / Assumptions:

• Rectangular waveform with equal high and low durations.
• Ideal edges and fixed period T.
• Symmetry about the mid-level.

Concept / Approach:
Rectangular waves become square waves when the duty cycle equals 50%, meaning the signal is high for T/2 and low for T/2 each period. Sawtooth and triangle waves vary linearly between levels; they are not rectangular. An impulse train consists of narrow pulses with low duty cycle, not 50% rectangular.

Step-by-Step Solution:
1) Identify waveform family: rectangular.2) Check duty cycle: D = 50% → high time equals low time.3) By definition, a 50% rectangular wave is a square wave.4) Conclude with the specific term “square wave”.

Verification / Alternative check:
Fourier series symmetry: a square wave contains only odd harmonics with 1/n amplitude, consistent with equal high/low symmetry; non-50% rectangular waves exhibit even harmonic content as well.

Why Other Options Are Wrong:
C wave: not a standard term.

Sawtooth: linear rise with sharp fall (or vice versa), not rectangular.

Triangle: symmetrical linear rise and fall, not flat tops/bottoms.

Impulse train: consists of very brief pulses, not 50% duty.

Common Pitfalls:
Assuming any rectangular wave is a square wave; 50% duty is the defining condition.

Final Answer:
square wave