Which of the following is a living cell which lacks nucleus on maturity ?

Options

A. Complementary cell
B. Mature sieve tube element
C. Mature vessel element
D. Companion cell

Answer

To solve the question "Which of the following is a living cell which lacks nucleus on maturity?", we need to analyze the options provided and understand the characteristics of each type of cell mentioned.

### Step-by-Step Solution:

1. **Understanding the Options**:
- Option 1: Complementary cell
- Option 2: Mature sieve tube element
- Option 3: Mature vessel element
- Option 4: Companion cell

2. **Analyzing Each Option**:
- **Complementary Cell**: This term is not commonly used in the context of plant cells and does not refer to a specific type of cell that fits the criteria of being living and lacking a nucleus at maturity.

- **Mature Sieve Tube Element**: Sieve tube elements are part of the phloem and are responsible for the transport of sugars. They are living cells but lose their nucleus at maturity to maximize the space available for transporting nutrients. This fits the criteria of the question.

- **Mature Vessel Element**: Vessel elements are part of the xylem and are responsible for water transport. These cells are dead at maturity, which disqualifies them from being the correct answer.

- **Companion Cell**: Companion cells are also part of the phloem and are closely associated with sieve tube elements. They are living cells that retain their nucleus even at maturity, thus they do not fit the criteria of lacking a nucleus.

3. **Conclusion**:
- Among the options, the **Mature Sieve Tube Element** is the only living cell that lacks a nucleus at maturity. Therefore, the correct answer is **Option 2: Mature Sieve Tube Element**.

### Final Answer:
The correct answer is **Option 2: Mature Sieve Tube Element**.