In a declining population, there are:

The correct answer is Option (1) → More individuals in the reproductive phase than in pre-reproductive phase

In a declining population the base of the pyramid (pre-reproductive individuals) is narrow, so there are fewer young than reproductive adults.

Option (1) More individuals in the reproductive phase than in pre-reproductive phase — Correct. A declining population has more individuals in the reproductive phase than in the pre-reproductive phase. Its age pyramid is narrow at the base, because few young are being added.

Option (2) Less individuals in the reproductive phase than in pre-reproductive phase — Incorrect. Fewer reproductive than pre-reproductive individuals means many young and a broad-based pyramid. That is a growing (expanding) population, not a declining one.

Option (3) More individuals in the reproductive phase than in post-reproductive phase — Incorrect. This holds for most populations and does not mark decline.

Option (4) Equal number of individuals in the reproductive as well as pre-reproductive phase — Incorrect. When pre-reproductive and reproductive individuals are about equal, the pyramid is bell-shaped. That marks a stable population, not a declining one.

NCERT Extract:
Population Attributes – “… A population at any given time is composed of individuals of different ages. If the age distribution (per cent individuals of a given age or age group) is plotted for the population, the resulting structure is called an age pyramid (Figure 11.1). For human population, the age pyramids generally show age distribution of males and females in a diagram. The shape of the pyramids reflects the growth status of the population - (a) whether it is growing, (b) stable or (c) declining.”