The correct answer is option 3: Tropical dry deciduous.

India is known for its rich diversity of forests and vegetation. Among the various types of forests present in India, the most widespread type is the tropical dry deciduous forest.

Tropical dry deciduous forests are found in regions that experience a pronounced dry season, typically during the winter months. These forests are characterized by a mix of deciduous trees that shed their leaves during this dry period. The trees in these forests are well-adapted to the dry conditions and have the ability to conserve water.

Mangrove forests, mentioned in option 1, are coastal wetland forests that are found in the coastal regions of India. While they are important and cover a significant area along the coasts, they are not as widespread as tropical dry deciduous forests.

Option 2, thorn-scrub, represents a type of vegetation rather than a type of forest. Thorn-scrub is characterized by the presence of thorny bushes and shrubs and is found in certain arid and semi-arid regions of India.

Option 4, tropical wet evergreen forests, is another important type of forest in India, but they are not as widespread as the tropical dry deciduous forests. Tropical wet evergreen