Ionospheric Propagation: For an F1 layer with maximum electron density Nmax = 2.3 × 10^4 electrons/cm^3, compute the critical frequency.

Introduction / Context:
Critical frequency is the highest frequency that will be reflected back to Earth by an ionospheric layer at normal incidence. It depends on peak electron density in that layer, a key parameter in HF radio communications.

Given Data / Assumptions:

• Nmax = 2.3 × 10^4 electrons/cm^3 (F1 layer).
• Use standard empirical relation for critical frequency at normal incidence.

Concept / Approach:
A common engineering rule is fo(MHz) ≈ 9 × √(Nmax), when Nmax is expressed in electrons/cm^3 (for a quick estimate). We directly substitute Nmax and compute fo.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

Common Pitfalls:

Final Answer: