The January isotherm taken as a basis for dividing India into tropical and subtropical zones is:
✓ Correct answer: b) 18°C
ExplanationThe 18°C January isotherm is used as the dividing line between the tropical and subtropical zones in India.This isotherm runs roughly along the Tropic of Cancer (23.5°N latitude) and helps distinguish the warmer tropical climate of southern India from the relatively cooler subtropical climate of northern India.Areas south of the 18°C isotherm (cover- ing most of Peninsular India) experience tropical climate with higher temperatures, minimal winter, and a distinct mon- soon pattern.Areas north of the 18°C isotherm (including northern states like Punjab, Haryana, and parts of Uttar Pradesh) fall under the subtropical zone, experiencing cooler winters and greater temperature variations between seasons.324
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