What physical quantity does the product of resistivity and conductivity depend on?

Resistivity ($\rho$) is a measure of how strongly a material opposes the flow of electric current.
Conductivity ($\sigma$) is a measure of how easily electric current flows through a material.

Conductivity is the reciprocal of resistivity.

The product of resistivity and conductivity is $\rho \times \sigma$.
Substitute the relationship from Step 2 into the product:

The product of resistivity and conductivity is always 1.

Since the product is always 1, it is a constant and does not depend on any physical properties like cross-sectional area, temperature, or length.

Comparing this with the given options:
[A] अनुप्रस्थ परिच्छेद क्षेत्र (Cross-sectional area)
[B] तापमान (Temperature)
[C] लंबाई (Length)
[D] इनमें से कोई नहीं (None of these)

The product does not depend on options [A], [B], or [C]. Therefore, the correct answer is [D].

The final answer is $\text{D}$.