What is the formula of exponential population growth curve ?

dN/dt= (b-d) x N

The correct answer is Option (2) - dN/dt= (b-d) x N

In exponential growth, resource (food and space) availability is obviously essential for the unimpeded growth of a population. Ideally, when resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number, as Darwin observed while developing his theory of natural selection. If in a population of size N, the birth rates (not total number but per capita births) are represented as b and death rates (again, per capita death rates) as d, then the increase or decrease in N during a unit time period t(dN/dt) will be:

dN/dt = (b – d) × N

Let (b–d) = r, then

dN/dt = rN

r in this equation is called the ‘intrinsic rate of natural increase’ and is a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth.