Standard resistivity of copper at room temperature Select the closest typical resistivity of copper at 20 °C, expressed with standardized SI units.

Introduction / Context:
Resistivity is a material property that determines how strongly a given material opposes electric current. For conductors like copper, knowing the typical resistivity at 20 °C is critical for wire sizing, power loss estimation, and signal integrity.

Given Data / Assumptions:

• Room temperature reference: 20 °C.
• Need an approximate, widely accepted value for copper.
• Use SI units (Ω·m) and convenient prefixes (nΩ·m).

Concept / Approach:
Copper's resistivity at 20 °C is commonly taken as about 1.68 × 10^-8 Ω·m. Expressed in nano-ohm-meters, this is approximately 16.8 nΩ·m. Engineering tables often round to about 17 nΩ·m for practical calculations, which is within typical tolerance and alloy variations.

Step-by-Step Solution:
Reference value: ρ ≈ 1.68 × 10^-8 Ω·m.Convert to nΩ·m: 1.68 × 10^-8 Ω·m = 16.8 nΩ·m.Round to standard tabulated value: ≈ 17.0 nΩ·m.Therefore, 17.0 nΩ·m is the best choice.

Verification / Alternative check:
Compare with common handbooks and cable datasheets; most list values near 1.68 × 10^-8 Ω·m at 20 °C with small variations depending on purity.

Why Other Options Are Wrong:
9.9 nΩ·m and 10.7 nΩ·m: too low for copper at 20 °C.16.7 nΩ·m: close but slightly low; 17.0 nΩ·m is the typical rounded reference.

Common Pitfalls:
Mixing units such as μΩ·cm and Ω·m; always convert to a consistent SI unit before comparison.

Final Answer:
17.0 nΩ·m