Which statement is correct

Options

A. Mycoplasma is smallest and wall less living organism
B. Influenza and herpes caused by virus having DNA and RNA
C. Nostoc and Anabaena are important decomposer
D. Methanogen are methane producing bacteria in wheat crop

Answer

To solve the question, we need to evaluate each statement provided in the options and determine which one is correct.

### Step-by-Step Solution:

1. **Evaluate the First Statement:**
- **Statement:** Mycoplasma is the smallest and wall-less living organism.
- **Analysis:** Mycoplasma are indeed the smallest known living cells and they lack a cell wall. They are prokaryotic microbes and can survive without oxygen. Their size ranges from approximately 150 to 250 nanometers. This statement is **correct**.

2. **Evaluate the Second Statement:**
- **Statement:** Influenza and herpes are caused by viruses having DNA and RNA.
- **Analysis:** Influenza is caused by the influenza virus, which has a genome composed of single-stranded RNA. Herpes is caused by the herpes simplex virus, which contains double-stranded DNA. Therefore, the statement is partially correct but misleading as it implies both viruses have DNA, which is not true. This statement is **incorrect**.

3. **Evaluate the Third Statement:**
- **Statement:** Nostoc and Anabena are important decomposers.
- **Analysis:** Nostoc and Anabena are types of cyanobacteria known for their ability to fix nitrogen, not for decomposition. Therefore, this statement is also **incorrect**.

4. **Evaluate the Fourth Statement:**
- **Statement:** Methanogens are methane-producing bacteria in wheat crops.
- **Analysis:** Methanogens are indeed methane-producing bacteria, but they primarily reside in the digestive tracts of ruminant animals and not in wheat crops. This statement is **incorrect**.

5. **Conclusion:**
- After evaluating all the statements, the only correct statement is the first one: "Mycoplasma is the smallest and wall-less living organism."

### Final Answer:
The correct statement is: **Mycoplasma is the smallest and wall-less living organism.**

---