What is the formula for exponential population growth?

Which model is considered a more realistic one?

In which phase is the maximum growth rate observed?

The apex of the age pyramid of a stationary population is

Assertion: In a sigmoid growth curve,the population finally stabilizes itself.
Reason: Finally,the death rate increases more than the birth rate.

In a population,if the number of post-reproductive age organisms is more than the reproductive age organisms,what will be the result for the population?