Logic family prefixes: The ________ prefix on integrated circuits denotes a broader (often military-grade) operating temperature range and is commonly used for defense/aerospace applications.

Introduction / Context:
Classic 54/74-series numbering distinguishes environmental qualifications. Selecting the correct series ensures reliable operation under the expected temperature extremes and conditions.

Given Data / Assumptions:

• 54-series traditionally indicates extended temperature range (e.g., around −55 °C to +125 °C).
• 74-series is typically commercial/industrial, depending on suffix.
• 2N is a discrete transistor prefix, not a logic family series.

Concept / Approach:
Recognize that “54” corresponds to military/extended temperature logic, whereas “74” is commercial/industrial logic families (TTL/CMOS variants). “TTL” is a technology class, not a prefix level; HCT denotes CMOS with TTL-compatible thresholds but uses 74HCTxx part numbers.

Step-by-Step Solution:

Verification / Alternative check:
Compare datasheets of 54HCxx vs 74HCxx: operating ranges and screening differ, but logical function/pinouts are typically aligned.

Why Other Options Are Wrong:

• 2N: Prefix for discrete transistors.
• 74: Commercial/industrial range, not the broader military range.
• TTL: Technology class, not a series prefix.
• HCT: A subfamily (74HCTxx), not the temperature-grade prefix in question.

Common Pitfalls:
Assuming 74 always means 0–70 °C; industrial variants exist, but “54” is the canonical military/extended indicator.

Final Answer:
54