Explanation:

The Ganga-Brahmaputra basin is a region in India and Bangladesh that is known for its rich biodiversity, including a variety of tropical deciduous trees. However, one of the options given, Mahogany, is not typically found in this region.

Tropical Deciduous Trees:
Tropical deciduous trees are trees that shed their leaves during a certain season, usually during the dry season. These trees are well-adapted to the tropical climate and are found in various regions, including the Ganga-Brahmaputra basin.

Ganga-Brahmaputra Basin:
The Ganga-Brahmaputra basin is a vast river basin in India and Bangladesh that includes the Ganges and Brahmaputra rivers. This region is known for its fertile soil and diverse flora and fauna.

Options:
a) Teak: Teak is a tropical deciduous tree that is commonly found in the Ganga-Brahmaputra basin. It is known for its high-quality timber and is widely used in furniture making.

b) Peepal: Peepal, also known as the sacred fig, is another tropical deciduous tree commonly found in the Ganga-Brahmaputra basin. It is considered sacred in many cultures and is often associated with religious significance.

c) Sal: Sal is a dominant species of tropical deciduous tree found in the Ganga-Brahmaputra basin. It is highly valued for its timber and is also known for its medicinal properties.

d) Mahogany: Mahogany, on the other hand, is not typically found in the Ganga-Brahmaputra basin. Mahogany trees are native to Central and South America and are not natural to the Indian subcontinent.

Inference:
Based on the information provided, the correct answer is option 'D' - Mahogany. While teak, peepal, and sal are commonly found in the Ganga-Brahmaputra basin, mahogany is not native to this region.