The correct option is Western Ghats.
Explanation
Amphibian diversity is strongly correlated with high humidity, abundant rainfall, and dense vegetation cover. In India, biogeographic zones that sustain tropical rainforests and stable aquatic ecosystems exhibit the highest species richness and endemism for amphibians.
Region-wise Analysis:
- Western Ghats: This region is a global biodiversity hotspot. Due to heavy rainfall from the southwest monsoon and the presence of tropical evergreen and semi-evergreen forests, it provides the ideal moist microhabitats required for amphibians. It hosts the highest diversity and endemism of amphibian species in India.
- Eastern Ghats: These are discontinuous hill ranges with a comparatively drier climate and vegetation (mostly dry deciduous). While they support biodiversity, the amphibian species richness is significantly lower than that of the Western Ghats due to lower precipitation and humidity.
- Aravallis: This is an old fold mountain range located in an arid to semi-arid region. The lack of sufficient moisture and forest cover results in very low amphibian diversity.
- Deccan Plateau: This region is largely semi-arid with dry deciduous forests and scrublands. It supports a moderate number of species but lacks the high diversity found in the wet zones.
- Gangetic Plains: While this region has abundant water resources, the habitat is largely homogenous and heavily modified by agriculture. It does not support the high level of speciation seen in the Western Ghats.
Key Takeaway: The Western Ghats exhibit the greatest diversity of amphibian species in India, driven by the region's high rainfall and complex tropical forest ecosystems.