Which of the following means of transport is cheapest for carrying heavy and…

Concept: The cost of moving cargo by a given mode depends on how much load a single trip can carry relative to the fuel and infrastructure it consumes; a mode that carries a very large tonnage per trip with low friction spends less fuel per tonne of cargo, which makes it the most economical choice for heavy, bulky goods over long distances.

Application: Ships and barges are supported by the buoyant force of water, so a single vessel can carry thousands of tonnes of cargo in one trip while using comparatively little fuel per tonne carried. This is why national geography curricula (for example, NCERT Class VI Geography) describe waterways as the cheapest means of transport for carrying heavy and bulky goods over long distances — matching the situation in this question, so Waterways is the correct choice.

Cross-check: Comparing the remaining modes for the same task confirms this:

• Railways — economical for bulk cargo over land wherever a rail line connects the origin and destination, but building and maintaining the rail network is capital-intensive and railways cannot reach every location.

• Roadways — offer door-to-door delivery without transshipment, which suits short and medium hauls, but a truck's engine has to overcome more friction per tonne of load than a waterborne vessel, raising the cost of moving heavy goods over long distances.

• Airways — the fastest mode, but keeping an aircraft airborne needs continuous high-power thrust, which consumes a large amount of fuel per tonne of cargo, so air transport is reserved for light or time-critical goods rather than heavy, bulky consignments.

None of the other three modes matches the combination of very large per-trip capacity and low friction that keeps water transport's cost per tonne of cargo the lowest, so Waterways is the mode best suited for carrying heavy and bulky goods cheaply over long distances.