In some members of which of the following pairs of families, pollen grains retain their viability for months after release ?

The correct answer is Rosaceae ; Leguminosae.

Explanation:
Pollen viability refers to the period for which pollen grains remain functional and capable of germinating on a compatible stigma to perform fertilization. This duration varies greatly among different plant species and is influenced by environmental conditions such as temperature and humidity.

1. Short Viability (Family Poaceae):
In cereal plants belonging to the family Poaceae (such as wheat and rice), pollen grains are highly sensitive and lose their viability very rapidly, usually within 30 minutes of their release.

2. Extended Viability (Families Rosaceae, Leguminosae, and Solanaceae):
In contrast, members of families such as Rosaceae (rose family), Leguminosae (pea/legume family), and Solanaceae (nightshade family) have pollen grains that are much more resilient. They can remain viable for several months under natural conditions.

Since the question asks for a pair of families in which pollen grains retain viability for months, the correct combination is Rosaceae ; Leguminosae.