The main objective of sustainable tourism is

Option C is correct. The UNWTO defines sustainable tourism as tourism that takes full account of its current and future economic, social and environmental impacts, while meeting the needs of visitors, host communities and the environment. The objective is balance: protect ecological processes and cultural integrity so that the destination stays viable for future generations.

Why the others fail:

• A is a growth goal. Sustainability asks whether a destination can carry its visitors, not how to raise arrivals. Unchecked growth is exactly what damages fragile sites.
• B describes scale, not an objective. Size alone does not decide sustainability: a small resort can be damaging and a large destination can be well managed.
• D is wrong because C states the objective correctly.

Core concept: carrying capacity. Every destination has limits of water, waste, habitat and community tolerance, and sustainable tourism works within them. For Mains GS-I and GS-III, link this to Himalayan hill stations, Ladakh's fragile ecology and community-based ecotourism.

Trap: choosing B because 'small scale' sounds green. The question asks for the objective, which is balancing environment, culture and ecology, not the size of tourism activity.