Which of the following statements is wrong for viroids?

Options

A. They lack a protein coat
B. They are smaller than viruses
C. They causes infections
D. Their RNA is of high molecular weight

Answer

To determine which statement about viroids is incorrect, we will analyze each statement provided:

1. **They lack a protein core.**
- This statement is true. Viroids do not have a protein coat (capsid) like viruses. They consist solely of a short strand of RNA.

2. **They are smaller than viruses.**
- This statement is also true. Viroids are indeed smaller than most viruses, making them one of the smallest known infectious agents.

3. **They cause infections.**
- This statement is true as well. Viroids are known to cause various plant diseases, such as the Potato Spindle Tuber Disease.

4. **Their RNA is of high molecular weight.**
- This statement is false. The RNA of viroids is actually of low molecular weight, not high. This is a key characteristic that distinguishes viroids from other infectious agents.

Based on this analysis, the incorrect statement about viroids is: **Their RNA is of high molecular weight.**

### Step-by-Step Solution:
1. **Identify the statements provided about viroids.**
2. **Evaluate each statement for accuracy.**
- Confirm that viroids lack a protein coat.
- Confirm that viroids are smaller than viruses.
- Confirm that viroids cause infections.
- Check the molecular weight of viroid RNA.
3. **Determine which statement is incorrect.**
4. **Conclude that the incorrect statement is about the RNA being of high molecular weight.**