Which one of the following families has features like bisexual, pentamerous, gamopetalous corolla with epipetalous stamens, sagittate anthers, subapocarpous ovary and a pair of follicles as their diagnostic characters.
A. Malvaceae
B. Leguminosae
C. Musaceae
D. Apocynaceae

Hint: The Apocynaceae family of flowering plants comprises trees, shrubs, herbs, stem succulents, and vines, and is often known as the dogbane family due to the use of some taxa as dog poison. The former Asclepiadaceae family is now considered a subfamily of the Apocynaceae family.
Many species grow as large trees in tropical forests, whereas others thrive in xeric (dry) tropical conditions. Perennial herbs from temperate zones can also be found. Many of these plants produce milky latex, and many of them are toxic if eaten; the family is rich in genera that contain alkaloids and cardiac glycosides, the latter of which are frequently used as arrow poisons.

Complete answer:
Option A: Milky latex, scales on the neck of the corolla tube, no pollinia, carpels with free ovaries, joined styles, follicular fruit, and seed with a tuft of hairs are all characteristics of Apocynaceae plants. Other traits include a bisexual, pentamerous, gamopetalous flower with epipetalous stamens.
So, option A is incorrect.
Option B: The bisexual, pentamerous, gamopetalous corolla of the Apocynaceae has epipetalous stamens, sagittate anthers, a subapocarpous ovary, and two follicles.
So, option B is not correct.
Option C: Plants in the Apocynaceae family have milky latex, scales on the throat of the corolla tube, no pollinia, carpels with free ovaries, united styles, follicular fruit, and seed with a tuft of hairs. Bisexual, pentamerous, gamopetalous corolla with epipetalous stamens are among the other characteristics.
So, option C is not correct.
Option D: The bisexual, pentamerous, gamopetalous corolla of the Apocynaceae has epipetalous stamens, sagittate anthers, a subapocarpous ovary, and two follicles.
Plants of the Malvaceae family have a bisexual corolla, a monadelphous androecium, unilocular anthers, big pollen, and a superior ovary.
Leguminosae plants have a bisexual, zygomorphic corolla, free, monadelhpus or didelphous androecium, unicarpelate, and superior ovary.
So, option D is correct.

Hence, Option D. is the correct answer.

Note:
Characters of apocynaceae:
Herbs, shrubs, and trees, often twining, with white latex; leaves are alternating, simple, exstipulate, generally opposite or whorled, with latex on the entire margin; Flowers hermaphrodite, actinomorphic, hypogynous; calyx free or joined; corolla gamopetalous, campanulate or funnel-shaped, valvate or twisted; androecium epipetalous, introrse; gynoecium bicarpellary, syncarpous, ovary superior; fruit-follicle or berry; seeds with crown of hairs.