Question

The pineapple which under natural conditions is difficult to blossom has been made to produce fruits throughout the year by application of
A. IAA, IBA
B. Phenylacetic acid
C. NAA, 2,4-D
D. Cytokinin

Answer 1

Hint: Auxin hormones promote flowering. In the pineapple plants, synthetic auxins may be applied to produce fruit throughout the year.

Complete answer: Auxin is a plant hormone that controls various growth and developmental processes in plants.
There are several variations of auxin including IAA and IBA. IAA is Indole acetic acid and IBA is Indole butyric acid. These have been isolated from plants.
NAA and 2,4-D are also auxin hormones but the difference is that these are synthetic versions. The full form of NAA is Naphthalene acetic acid and 2,4-D means 2,4 dichlorophenoxyacetic acid.
These are used in agriculture and gardening as rooting hormones and help in plant propagation. Moreover, they also promote flowering in plants, e.g. in pineapples.

So, the correct option is C. NAA, 2,4-D

Note: Phenylacetic acid is just an organic compound.
It is not a plant hormone.
It has a honey-like odor.
Cytokinins are growth promoters that stimulate cell-division and cytokinesis in cells of root and shoots of plants.