**Core Concept**
Life expectancy is a widely used demographic indicator that measures the average number of years a person from a specific population is expected to live. It is a key indicator of a population's health status and is influenced by various factors such as mortality rates, fertility rates, and disease prevalence.

**Why the Correct Answer is Right**
Life expectancy is a mortality indicator because it directly reflects the average lifespan of a population. It takes into account the number of deaths occurring within a population over a specified period, which makes it a reliable measure of mortality rates. Life expectancy is often used as an indicator of a country's overall health and well-being, with higher life expectancy rates typically indicating better health outcomes.

**Why Each Wrong Option is Incorrect**
**Option B:** Notification rate is a measure of the number of cases of a specific disease reported to health authorities within a given period, but it does not directly reflect mortality rates. It is primarily used as an indicator of disease prevalence.

**Option C:** Disability-Adjusted Life Years (DALYs) are a measure of the burden of disease, which takes into account both mortality and morbidity. While DALYs do reflect the impact of mortality, they are not a direct mortality indicator.

**Option D:** Bed turn-over ratio is a measure of hospital efficiency, indicating the number of patients admitted and discharged within a specified period. It is not a direct indicator of mortality rates.

**Clinical Pearl / High-Yield Fact**
Remember that life expectancy is a lagging indicator, meaning it reflects changes in mortality rates that have already occurred. It is essential to monitor and track life expectancy trends to identify areas for improvement in public health.

**✓ Correct Answer: A. Life Expectancy**