Identity the group of organisms, on the basis of given informations * Show symbiotic association
* Very good pollution indicator
* Pioneer to barren rocks

Answer

To identify the group of organisms based on the given information, we will analyze each point provided in the question step by step.

### Step 1: Understand Symbiotic Association
The first clue states that the organisms show a symbiotic association. Symbiosis is a close and often long-term interaction between two different biological species. In many cases, this relationship is mutualistic, meaning both organisms benefit from the association.

**Hint:** Look for organisms that have a mutualistic relationship with another species.

### Step 2: Identify Pollution Indicators
The second clue mentions that these organisms are very good pollution indicators. This means that they are sensitive to pollution levels in their environment and can indicate the health of the ecosystem. Organisms that are good pollution indicators often thrive in clean environments and decline in polluted areas.

**Hint:** Consider organisms that are sensitive to specific pollutants and can only thrive in clean conditions.

### Step 3: Recognize Pioneer Species
The third clue states that these organisms are pioneers to barren rocks. Pioneer species are the first organisms to colonize previously uninhabited or disturbed environments. They play a crucial role in ecological succession, helping to create conditions suitable for other species to thrive.

**Hint:** Think about organisms that are known to be the first to grow in harsh environments, such as bare rock.

### Step 4: Synthesize Information
Now, let’s synthesize the information from the three clues:
- The organisms show a mutualistic relationship (symbiotic association).
- They are sensitive to pollution and serve as indicators of environmental health.
- They are pioneers that can colonize barren rocks.

### Step 5: Identify the Organism
The group of organisms that fits all these criteria is **lichens**. Lichens are a symbiotic association between fungi and algae (or cyanobacteria). They are known to be excellent indicators of air quality, particularly sensitive to sulfur dioxide pollution. Additionally, lichens are often the first organisms to colonize bare rocks, contributing to soil formation and paving the way for other plants.

**Final Answer:** The group of organisms is **lichens**.