In demography, most concepts are expressed in which of the following…

The correct answer is Option (4) → Rates or ratios involving two numbers

Option (1) Projections of future population size — Incorrect. A projection is an estimate of how large a population may become in future. It is a forecast of a size, and it does not set one number against another.

Option (2) Absolute totals counted at each census — Incorrect. An absolute total is a raw count, such as the number of births in a year. A raw count cannot be compared across areas of different size, so concepts are not expressed this way.

Option (3) Averages drawn from sample surveys — Incorrect. A sample survey collects data from a part of the people in a territory, and an average sums those data up in one figure. One figure alone gives no second number to judge it by, so it is not the usual form of a demographic concept.

Option (4) Rates or ratios involving two numbers — Correct. Most demographic concepts are rates or ratios with two numbers. One is the statistic for a particular area, and the other gives a standard for comparison.