The mechanical tissue with high refractive index is
(a) Collenchyma
(b) Prosenchyma
(c) Sclerenchma
(d) Sclereids

Options

A. Collenchyma
B. Prosenchyma
C. Sclerenchma
D. Sclereids

Answer

To determine the mechanical tissue with a high refractive index, we need to analyze the options provided:

1. **Collenchyma**: This tissue is composed of living cells that have irregularly thickened cell walls. The thickening is primarily due to the presence of pectin, cellulose, and hemicellulose. These materials contribute to a higher refractive index because they are more complex and denser than the materials found in other types of mechanical tissues.

2. **Prosenchyma**: This term is not commonly used in plant anatomy. It may refer to a type of tissue that is not well-defined in terms of mechanical support and does not have a high refractive index.

3. **Sclerenchyma**: This tissue is made up of dead cells that have thick, lignified walls. While they provide mechanical support, the dead nature of these cells and the composition of their walls do not contribute to a high refractive index.

4. **Sclereids**: These are a type of sclerenchyma cell that also has thick, lignified walls. Like sclerenchyma, they are dead cells and do not have a high refractive index.

Based on the analysis, the correct answer is **(a) Collenchyma**. This tissue is characterized by living cells with irregularly thickened walls, which results in a high refractive index.

### Summary of Steps:
1. Identify the types of mechanical tissues listed in the options.
2. Analyze the characteristics of each tissue type.
3. Determine which tissue has living cells and irregularly thickened walls.
4. Conclude that Collenchyma has a high refractive index due to its composition.