Question

Which among the following is a nitrogen-fixing bacteria - (A) Rhizobium
(B) Azotobacter
(C) Azospirillum
(D) Streptococcus
Choose the correct answer from the options given below:

• A. (A), (B) and (C) only
• B. (A), (B) and (D) only
• C. (A), (B), (C) and (D)
• D. (B), (C) and (D) only

Hint:

Symbiotic nitrogen fixers (e.g., Rhizobium) live in plant roots, while free-living fixers (e.g., Azotobacter, Azospirillum) live independently in the soil.

Answer 1

The Correct Option is A

Step 1: Recall nitrogen-fixing bacteria.
- Rhizobium: Symbiotic nitrogen fixer found in root nodules of legumes.
- Azotobacter: Free-living nitrogen fixer present in soil.
- Azospirillum: Free-living nitrogen fixer, commonly associated with grasses.
- Streptococcus: A pathogenic bacterium, not involved in nitrogen fixation.

Step 2: Construct the correct set.
Thus, nitrogen-fixing bacteria are (A), (B), and (C).

Step 3: Verify options.
This matches with Option 1.

Final Answer: \[ \boxed{\text{The correct answer is 1. (A), (B) and (C) only.}} \]