Q.Define 'zero population growth rate'. Draw a age pyramid for the same.

Zero population growth rate means the population size is stable -- it neither increases nor decreases -- because births plus immigration exactly balance deaths plus emigration. Each generation is simply replacing itself.

The age pyramid for a zero-growth (stationary) population is bell-shaped: the pre-reproductive and reproductive tiers are roughly the SAME width as each other (not narrower), and the pyramid only tapers inward near the very top, where old-age mortality thins the numbers. This is different from both the broad-based expanding pyramid (young >> old) and the narrow-based declining pyramid (young < old) -- here, the width stays rough …

Zero population growth is a demographic condition that many countries, especially in Europe and East Asia, are either approaching or have already entered. It is not the same as a static, unchanging society — people are still born, still die, and still move — but the net effect is zero change in total population size. For a closed population (no migration), this means the birth rate equals the death rate. For an open population, it means births plus in-migrants equals deaths plus out-migrants.

The concept is important because it tells us something fundamental about a society's age structure and future. A population that has achieved zero growth is not necessarily "young" or "old" — it can be either, depending on how it got there. But the age pyramid for a zero-growth population has a very distinctive shape.

The age pyramid for a zero population growth rate looks like a bell or a nearly vertical-sided structure. It is not a perfect rectangle because some mortality still occurs at every age — but the key feature is that the bars for the younger age groups (0–14 years) are roughly the same width as those for the middle and older age groups. There is no broad base of children, as in a growing population, and no narrow base, as in a declining one.

Imagine a pyramid where the base is not much wider than the middle. The 0–4 age group bar is about the same length as the 30–34 bar, and the 60–64 bar is only slightly shorter. This shape tells you that each generation is just replacing itself — parents have exactly enough children to take their place in the population when they die. There is no "bulge" of young people pushing upward, and no "bulge" of elderly people at the top (unless the population has recently transitioned from growth to zero growth, in which case a temporary bulge may exist). …

Set births + immigration exactly equal to deaths + emigration in the population-change equation first (so the net change is zero), then work out what age structure is consistent with that balance, r …