The Fungi Kingdom includes organisms that obtain nutrients by decomposing organic matter in their environment. This unique mode of nutrition distinguishes fungi from plants and animals.

The correct answer is option 'C', the Fungi Kingdom.

Fungi are a group of organisms that obtain nutrients by decomposing organic matter in their environment. They play a crucial role in the ecosystem as decomposers, breaking down dead organic material and recycling nutrients back into the environment. Here is a detailed explanation of why fungi belong to the kingdom that includes organisms obtaining nutrients through decomposition:

1. Fungi as decomposers:
- Fungi have a unique ability to break down complex organic compounds, such as cellulose and lignin, which are found in plant and animal tissues.
- They secrete enzymes that break down these complex molecules into simpler compounds that can be absorbed by the fungi as nutrients.
- This process of decomposition helps in the recycling of nutrients and the breakdown of dead organic matter.

2. Characteristics of Fungi:
- Fungi are eukaryotic organisms, meaning they have a true nucleus and membrane-bound organelles.
- They lack chlorophyll, which is necessary for photosynthesis, so they cannot produce their own food like plants.
- Instead, fungi obtain nutrients by absorbing organic matter from their surroundings.
- Fungi have a filamentous structure called hyphae, which allows them to grow and spread through their environment.

3. Other Kingdoms:
- The Plant Kingdom (option 'A') includes organisms that are capable of photosynthesis and produce their own food using sunlight, water, and carbon dioxide. They do not decompose organic matter for nutrition.
- The Animal Kingdom (option 'B') includes organisms that are heterotrophic, meaning they obtain nutrients by consuming other organisms. They do not decompose organic matter like fungi.
- The Protist Kingdom (option 'D') is a diverse group of eukaryotic microorganisms that do not necessarily obtain nutrients through decomposition. They can be photosynthetic, heterotrophic, or decomposers, but not all protists are decomposers like fungi.

4. Importance of Fungi:
- Fungi are essential for nutrient cycling in ecosystems as they break down dead organic matter and release nutrients back into the environment.
- They also form mutualistic relationships with plants, such as mycorrhizae, where they help in nutrient absorption by plant roots.
- Fungi have economic importance as they are used in food production (e.g., yeast for baking and brewing), medicine (e.g., antibiotics), and biotechnology.

In conclusion, the kingdom that includes organisms obtaining nutrients by decomposing organic matter in their environment is the Fungi Kingdom. Fungi play a vital role as decomposers in the ecosystem, breaking down dead organic material and recycling nutrients.