Point out the odd one from the given options.

The correct answer is Option (4) → Pollen grain

Three of the four terms are parts of the ovule, the female structure inside the ovary of a flower. The odd one is the term that belongs to the male side of the flower.

Option (1) Nucellus — Part of the ovule. The nucellus is the mass of cells enclosed within the integuments of the ovule. Its cells hold abundant reserve food.

Option (2) Embryo sac — Part of the ovule. The embryo sac is the female gametophyte. It is formed from a megaspore and lies inside the nucellus.

Option (3) Micropyle — Part of the ovule. The micropyle is the small opening at the tip of the ovule, where the integuments do not cover the nucellus.

Option (4) Pollen grain — Not a part of the ovule. Pollen grains are the male gametophytes. They are formed inside the microsporangia of the anther and are released when the anther opens, so they are the odd one out.

NCERT Extract:
The Pistil, Megasporangium (Ovule) and Embryo Sac – “… Each ovule has one or two protective envelopes called integuments. Integuments encircle the nucellus except at the tip where a small opening called the micropyle is organised. Opposite the micropylar end, is the chalaza, representing the basal part of the ovule. Enclosed within the integuments is a mass of cells called the nucellus. Cells of the nucellus have abundant reserve food materials. Located in the nucellus is the embryo sac or female gametophyte.”
Stamen, Microsporangium and Pollen Grain – “… Inside each microsporangium several thousands of microspores or pollen grains are formed that are released with the dehiscence of anther (Figure 1.3c). Pollen grain: The pollen grains represent the male gametophytes.”