**Core Concept**
The dependency ratio is a demographic measure that calculates the ratio of dependent individuals (children under 15 and elderly above 65) to the working-age population. Dependent individuals are those who are not economically productive and require support from the working-age population.

**Why the Correct Answer is Right**
To calculate the dependency ratio, we need to first calculate the number of dependents. In this population, there are 150 children under 15 and 50 elderly above 65, making a total of 200 dependents. The working-age population can be calculated as the total population minus the dependents. So, the working-age population is 1000 - 200 = 800. Now, we can calculate the dependency ratio by dividing the number of dependents by the working-age population and multiplying by 100 to get a percentage. Dependency ratio = (200 / 800) * 100 = 25%. Since the question asks for the ratio, we can express it as 0.25.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the dependency ratio is not 0.2. The correct ratio is 0.25, which is a 25% dependency ratio.
**Option B:** This option is incorrect because the dependency ratio is not 200. The correct ratio is 0.25, which is a percentage, not a number of individuals.
**Option D:** This option is incorrect because it is a multiple of the correct answer, but it is not the correct answer itself. The correct answer is 0.25, not 250.

**Clinical Pearl / High-Yield Fact**
The dependency ratio is an important indicator of the economic burden on the working-age population. A high dependency ratio can indicate a strain on the economy and a need for social security measures to support the dependent population.

**✓ Correct Answer: C. 0.25**