The cause of special flavour in onion and garlic is due to the presence of
Or
Yellowing of tea leaf takes place by the deficiency of

Options

A. Chlorine
B. Hydrogen
C. Oxygen
D. Sulphur

Answer

### Step-by-Step Solution:

1. **Identify the Compounds in Onion and Garlic**:
- Onions and garlic belong to the genus Allium.
- They are known for their distinctive flavors and aromas.

2. **Recognize the Key Chemical**:
- The special flavor in onion and garlic is attributed to sulfur-containing compounds, specifically sulfoxides.

3. **Understand the Chemical Reaction**:
- When onions are cut or peeled, the sulfoxides are converted into sulfenic acids through the action of an enzyme called alliinase.

4. **Link to the Flavor**:
- The sulfenic acids produced are responsible for the pungent odor and flavor associated with onions and garlic.

5. **Address the Second Part of the Question**:
- The yellowing of tea leaves is due to a deficiency of sulfur, which is crucial for the formation of proteins.
- Sulfur-containing amino acids, such as cysteine and methionine, are necessary for proper plant growth and development.

6. **Conclusion**:
- Both the special flavor in onion and garlic and the yellowing of tea leaves are linked to sulfur. Therefore, the correct answer for both parts of the question is sulfur.

### Final Answer:
- The cause of the special flavor in onion and garlic is due to the presence of **sulfur**.
- Yellowing of tea leaves takes place by the deficiency of **sulfur**.