**Core Concept**
Eutrophication is a process where water bodies become enriched with excess nutrients, leading to an overgrowth of algae and potentially harming aquatic life. This excess nutrient input can come from various sources, including agricultural runoff, sewage, and industrial waste.

**Why the Correct Answer is Right**
Phosphates and nitrates are the primary nutrients responsible for eutrophication. Phosphates stimulate the growth of algae, while nitrates serve as a nitrogen source for these microorganisms. When these algae die and decompose, they consume oxygen in the water, creating conditions that are harmful to other aquatic life. The excessive growth of algae also leads to the formation of "dead zones" where aquatic life cannot survive due to low oxygen levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Carbonates and oxides do not directly contribute to eutrophication. While they can affect water chemistry, their role is not as significant as that of phosphates and nitrates in promoting algal growth.

**Option B:** Hydrocarbons and metals can be pollutants in water bodies, but they are not the primary cause of eutrophication. Hydrocarbons can affect aquatic life through toxicity, while metals can accumulate in organisms and potentially cause harm.

**Option C:** Carbonates and sulphates can affect water chemistry, but they do not directly contribute to eutrophication. Carbonates can buffer pH levels, while sulphates can affect the availability of nutrients, but neither is as directly linked to eutrophication as phosphates and nitrates.

**Clinical Pearl / High-Yield Fact**
To prevent eutrophication, it's essential to implement measures that reduce the input of phosphates and nitrates into water bodies. This can be achieved through the proper management of agricultural runoff, sewage treatment, and industrial waste disposal.

**✓ Correct Answer: D. Phosphates and nitrate**