Option 1 states that mangrove plants are large wood-yielding trees of the tropical forests. This is incorrect because while mangroves can grow into large trees, they are not typically found in tropical forests. Mangroves are usually found in coastal areas and estuaries.

Option 2 correctly describes mangrove plants as plants that grow in marshy areas with breathing roots. This is because mangroves are uniquely adapted to live in saline, oxygen-poor conditions, and their breathing roots, called pneumatophores, help them obtain oxygen.

Option 3 states that mangrove plants are succulent plants that can thrive in arid/desert areas. This is incorrect because mangroves are not suited for arid or desert environments. They require specific conditions found only in coastal areas, such as high humidity and saltwater.

Option 4 describes vast grassland areas interspersed with deciduous trees and thorny bushes. This is unrelated to mangrove plants.

In conclusion, option 2 is the correct description of mangrove plants, as they are plants that grow in marshy areas with breathing roots.