The 74121 nonretriggerable one-shot (monostable multivibrator) can be configured so that the output pulse width is set by a single external component. Which component is used in that single-component timing configuration?

Introduction / Context:
Monostable multivibrators generate a single output pulse of controlled duration in response to a trigger. The 74121 (and similar families) offers flexible timing configurations. Knowing which external parts are required helps when selecting components for pulse-width generation in digital timing circuits.

Given Data / Assumptions:

• Device: 74121 nonretriggerable one-shot.
• Some configurations use both an external resistor and capacitor (R*C) to set pulse width.
• The device also provides an internal timing resistor path that allows using a single external capacitor for timing in a particular mode.

Concept / Approach:
The 74121 supports two timing modes: one using external R and C for a wide range of pulse widths, and another that leverages an internal resistor (selected by pin strapping) so that only an external capacitor determines the time constant. In that single-component mode, the external capacitor charges/discharges through the internal resistor to create the specified pulse width.

Step-by-Step Solution:

Verification / Alternative check:
Reviewing application notes for 74121/74LS121 shows the single-capacitor timing option, whereas the 74123 requires both R and C externally for timing.

Why Other Options Are Wrong:
Inductors are not used in these standard one-shot timing paths. A standalone resistor cannot define timing without a capacitor. An LED is unrelated to timing generation.

Common Pitfalls:
Confusing the 74121 (with optional internal resistor) and the 74123 (dual retriggerable one-shot requiring external R and C). Also, neglecting capacitor tolerance and temperature coefficients can skew pulse width.

Final Answer:
capacitor