On mountainous regions in India, which of the following railway lines are used?

Narrow Gauge

The correct answer is Option 4: Narrow Gauge

In mountainous regions of India, Narrow-gauge railway lines are commonly used because they can easily negotiate sharp curves and steep slopes found in hilly areas.

NCERT: On the basis of the width of track of the Indian Railways, three categories have been made:

Broad gauge: The distance between rails in broad gauge is 1.676 metre. The total length of broad gauge lines was 63950 km (2019-20).

Metre gauge: The distance between rails is one metre. Its total length was 2402 km (2019-20).

Narrow gauge: The distance between the rails in this case is 0.762 metre or 0.610 metre. The total length of narrow guage was 1604 km (2019-20). It is generally confined to hilly areas.