Rail sections on Metre Gauge — identify the rail section that is not used on Indian Metre Gauge (MG) tracks.

Introduction / Context:
Indian railways historically used designated rail sections (e.g., 30 R, 35 R, 40 R) on Metre Gauge (MG). Knowledge of which sections belong to MG versus Narrow Gauge (NG) or specific older practices is a standard objective-type topic in permanent way examinations.

Given Data / Assumptions:

• Common MG rail sections: 30 R, 35 R, 40 R.
• Very light sections like 25 R are typically associated with lighter-duty applications, often NG or older, low-traffic lines.
• We identify the section not used on MG from the given list.

Concept / Approach:

Metre Gauge requires sufficient rail weight to handle axle loads and speeds typical of MG operations. 30 R, 35 R, and 40 R have been mainstream on MG. The 25 R section is undersized for most MG permanent way standards and is traditionally not adopted for Indian MG tracks in regular service.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Older Indian railway manuals and exam syllabi consistently quote 30 R/35 R/40 R for MG; 25 R is absent from MG listings.

Why Other Options Are Wrong:

30 R, 35 R, and 40 R are well-known MG sections. 45 R is not a standard MG section but is not among the original options identified as “used”. Among the main four provided, 25 R is clearly the “not used”.

Common Pitfalls (misconceptions, mistakes):

Assuming all small-numbered sections are NG; overlooking that MG has specific well-documented section series.

Final Answer:

25 R