Timing with 74123 retriggerable monostable — find the output pulse width (t_w). Given: R_ext = 4.7 kΩ, C_ext = 0.022 µF (22 nF). Select the closest value of t_w for a standard 74x123 device.

Introduction / Context:
Monostable multivibrators (one-shots) such as the 74x123 produce a single output pulse whose width is set by an external resistor and capacitor. This question tests whether you know the proper timing constant for the 74123 family and can convert units correctly.

Given Data / Assumptions:

• IC: 74123 (retriggerable monostable)
• R_ext = 4.7 kΩ
• C_ext = 0.022 µF = 22 nF
• Use the typical 74123 timing relation t_w ≈ K * R_ext * C_ext, where K is about 0.32 to 0.45 depending on the specific logic family and operating conditions.

Concept / Approach:
For the 74123, many datasheets give a nominal constant near 0.32 for common trigger/configurations. Therefore compute RC first, then apply K ≈ 0.32 for a close estimate of pulse width.

Step-by-Step Solution:

Verification / Alternative check:
If K were as high as 0.45, t_w would be ≈ 46.5 µs. Options provided include 33.3 µs and 46.5 µs; however, the most widely quoted nominal for the 74123 timing is close to 0.32 in many reference problems, so 33.3 µs is the best match to typical expectations.

Why Other Options Are Wrong:

• 290 ms and 29 ms: These are orders of magnitude larger than any K * RC with the given components.
• 290 µs: Would require K ≈ 2.8, not applicable.
• 46.5 µs: Uses K ≈ 0.45; while possible in some families, the common nominal answer for this setup is lower.

Common Pitfalls:

• Confusing the 74123 constant with the 555 monostable constant (≈ 1.1).
• Unit mistakes when converting µF to F or kΩ to Ω.

Final Answer:
33.3 µs