Question

Identify the following organism which is a symbiotic nitrogen fixer?

• A. Azotobacter
• B. Rhizobium
• C. Clostridium
• D. Nitrosomonas

Hint:

Remember the important nitrogen-fixing bacteria: \[ \boxed{ \begin{aligned} \textit{Rhizobium} &\rightarrow \text{Symbiotic} \textit{Azotobacter} &\rightarrow \text{Free-living aerobic} \textit{Clostridium} &\rightarrow \text{Free-living anaerobic} \end{aligned} } \]

Answer 1

The Correct Option is B

Step 1: Recall the types of nitrogen-fixing organisms. Nitrogen-fixing bacteria are classified as
• Free-living nitrogen fixers,
• Symbiotic nitrogen fixers.

Step 2: Identify the symbiotic nitrogen fixer. \[ \begin{aligned} \textit{Azotobacter} &\rightarrow \text{Free-living aerobic nitrogen fixer}, \textit{Clostridium} &\rightarrow \text{Free-living anaerobic nitrogen fixer}, \textit{Nitrosomonas} &\rightarrow \text{Nitrifying bacterium}, \textit{Rhizobium} &\rightarrow \text{Symbiotic nitrogen fixer}. \end{aligned} \] Rhizobium lives in the root nodules of leguminous plants and fixes atmospheric nitrogen. Hence, \[ \boxed{\textit{Rhizobium}} \] is the correct answer. Therefore, \[ \boxed{(B)} \] is the correct answer.