For a Unijunction Transistor (UJT), the intrinsic stand-off ratio (η) is a key parameter. Select a typical value most commonly assumed in introductory analyses and design estimates.

Introduction / Context:
The intrinsic stand-off ratio η of a UJT determines the emitter firing voltage relative to the interbase voltage. Designers often assume a nominal η for first-pass timing and relaxation oscillator calculations.

Given Data / Assumptions:

• Standard UJT behavior (e.g., 2N2646 family).
• η is device-dependent but typically falls within a range.

Concept / Approach:
η ≈ R_B1 / (R_B1 + R_B2) and typically lies around 0.5 to 0.8. Using η ≈ 0.6 is a common textbook nominal for calculating the approximate peak-point voltage V_P = η * V_BB + V_D (small diode term).

Step-by-Step Solution:
1) Recognize η as a ratio inherent to the UJT structure.2) Typical values cluster around 0.6–0.7; using 0.6 is a standard assumption.3) Choose the nearest standard value provided.
Verification / Alternative check:
Datasheets show spreads, but application notes often compute with η ≈ 0.6 for relaxed design accuracy.

Why Other Options Are Wrong:

• 0.1, 0.2: Too low for typical UJTs; would result in very low trigger points.
• 0.9: Too high; most devices do not exhibit such a large stand-off ratio.
• 0.3: Still low relative to common practice.

Common Pitfalls:

• Treating η as constant across all units; it varies with device and temperature.
• Ignoring the small diode drop term V_D in V_P calculations.

Final Answer:
η ≈ 0.6 (Option C).