Rule-of-thumb relationship: On Indian Railways, the ratio of axle load (tonnes) to rail weight (kg/m) commonly used for selection checks is approximately:

Introduction / Context:
Preliminary rail selection often uses a quick check relating axle load (in tonnes) to rail section mass (in kg per metre). This rule-of-thumb does not replace full structural analysis but provides a fast screening for suitability.

Given Data / Assumptions:

• Axle load expressed in tonnes.
• Rail section weight expressed in kg/m.
• Heuristic ratio used in Indian practice for initial checks.

Concept / Approach:
The empirical relation approximates the practical capacity of a rail section. A value near 5/12 (≈ 0.417) has long been referenced to ensure the rail mass is commensurate with expected axle loads, pending detailed verification (section modulus, speeds, sleeper density, maintenance standards).

Step-by-Step Solution:
1) Express a screening ratio for quick selection.2) Adopt the commonly cited 5/12 value.3) Use it to verify that a chosen rail weight is reasonable for the planned axle loads.

Verification / Alternative check:
Compare with known practice: heavier rails (52–60 kg/m) support higher axle loads (≈ 20–25 t), which align with the 5/12 screening magnitude when converted consistently.

Why Other Options Are Wrong:

• 3/12 or 4/12 are too low and may understate required rail mass.
• 6/00 is not a meaningful ratio in this context.
• None of these is incorrect because 5/12 is the recognized rule-of-thumb figure.

Common Pitfalls:

• Treating the ratio as a code requirement; it is only an initial guide and must be followed by detailed design checks.

Final Answer:
5/12.