Step 1: Understanding Age Pyramids and Population Growth.
An age pyramid graphically represents a population's age distribution, with its shape indicating growth status.
Step 2: Analyzing the Scenario.
- Expanding (Option 1): A population expands if the reproductive age group is larger than the pre-reproductive group. This is characterized by a broad base and narrow top on the age pyramid, signifying a high birth rate and future growth potential.
- Stable (Option 2): A stable population exhibits a uniform age group distribution, lacking a disproportionate reproductive age group.
- Declining (Option 3): A declining population has more individuals in older age brackets and fewer in reproductive or pre-reproductive groups.
- Homeostasis (Option 4): Homeostasis, a state of internal balance, is not directly linked to population growth.
Step 3: Conclusion.
The correct answer is Expanding, as an excess in the reproductive age group signals population growth.
Final Answer: \[\boxed{\text{The correct answer is (1) Expanding.}}\]