Select correct statements for algae.
(i) They have thalloid body with adventitious roots.
(ii) Form and size is highly variable.
(iii) At least a half of the total `CO_(2)` fixation on earth is carried out by these organisms.
(iv) Green algae and brown algae produce large amounts of hydrocolloids .

Options

A. I & III
B. I,II & III
C. II, III & IV
D. II & III

Answer

To determine the correct statements regarding algae, let's analyze each statement step by step.

### Step 1: Analyze Statement (i)
**Statement (i): They have thalloid body with adventitious roots.**
- Algae typically have a thalloid body, which means they do not have true stems, leaves, or roots like higher plants. Instead, they have structures that perform similar functions. However, the term "adventitious roots" is not commonly used for algae, as they do not possess true roots. Therefore, this statement is **incorrect**.

### Step 2: Analyze Statement (ii)
**Statement (ii): Form and size is highly variable.**
- Algae exhibit a wide range of forms and sizes, from microscopic phytoplankton to large seaweeds. This statement is **correct**.

### Step 3: Analyze Statement (iii)
**Statement (iii): At least a half of the total CO₂ fixation on earth is carried out by these organisms.**
- Algae play a significant role in global carbon fixation through photosynthesis. It is estimated that a substantial portion of the Earth's CO₂ fixation is attributed to algae, particularly marine algae. This statement is **correct**.

### Step 4: Analyze Statement (iv)
**Statement (iv): Green algae and brown algae produce large amounts of hydrocolloids.**
- Hydrocolloids are substances that can hold water and are produced by certain algae. While brown algae (such as kelp) and red algae produce hydrocolloids (like algin and carrageenan), green algae do not produce significant amounts of hydrocolloids. Therefore, this statement is **incorrect**.

### Conclusion:
The correct statements regarding algae are:
- **Statement (ii)**: Form and size is highly variable.
- **Statement (iii)**: At least a half of the total CO₂ fixation on earth is carried out by these organisms.

### Final Answer:
The correct statements are (ii) and (iii).

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