Explanation:

- The Gini index measures income inequality within a population. It ranges from 0 to 1, where 0 indicates perfect equality and 1 indicates maximal inequality.

$$\textcolor{green}{\text{}}$$ Correct Answer: Option 1 - Income Inequality

- Option 2 - Infant Mortality Rate: This measures the number of infant deaths per 1,000 live births. It reflects the health conditions and medical care quality but is not related to the Gini index.

- Option 3 - Health: While health can influence and be influenced by economic factors, the Gini index directly addresses income distribution, not health metrics.

- Option 4 - Education: Education impacts and is impacted by income levels but is not directly measured by the Gini index itself.