Which of the following parasites is nonliving outside the cell of a living organism and becomes living on entering it ?

Options

A. Bacteria
B. Bacteriophage
C. Plasmodium
D. None of these

Answer

To solve the question "Which of the following parasites is nonliving outside the cell of a living organism and becomes living on entering it?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for a parasite that is nonliving outside of a host cell and becomes living once it enters the host. This implies we are looking for a type of parasite that relies on a host for its life processes.

2. **Analyze the Options**: The options provided are:
- A) Bacteria
- B) Bacteriophage
- C) Plasmodium
- D) None of these

3. **Evaluate Each Option**:
- **A) Bacteria**: Bacteria are living organisms that can survive independently outside of a host. They do not fit the criteria of being nonliving outside a host.
- **B) Bacteriophage**: Bacteriophages (or phages) are viruses that specifically infect bacteria. They are considered nonliving outside of a host cell because they cannot carry out metabolic processes on their own. Once they enter a bacterial cell, they hijack the host's machinery to replicate, thus becoming "living" in a sense within the host.
- **C) Plasmodium**: Plasmodium is a genus of parasitic protozoa that causes malaria. It is a living organism and does not fit the description of being nonliving outside a host.
- **D) None of these**: This option implies that none of the other options are correct.

4. **Select the Correct Answer**: Based on the analysis, the correct answer is **B) Bacteriophage**. Bacteriophages are nonliving outside of a host and become active once they infect a bacterial cell.

### Final Answer:
**B) Bacteriophage**