To solve the question using the provided dichotomous key, we will follow the steps outlined in the video transcript.
### Step-by-Step Solution:
1. **Identify the Type of Disease**:
- The first question in the key asks whether the disease is a vitamin deficiency disease or a mineral deficiency disease.
- Since we have options P, Q, R, and S, we will analyze each one based on the key.
2. **Analyze P**:
- According to the key, P is characterized by "bleeding gums and aching joints."
- This symptom is indicative of **scurvy**, which is caused by a deficiency of **Vitamin C**.
- Therefore, **P = Scurvy (Vitamin C deficiency)**.
3. **Analyze Q**:
- Q is characterized by "red rashes, scaly lesions on skin, diarrhoea, dementia, etc."
- These symptoms are associated with **pellagra**, which is caused by a deficiency of **Vitamin B3 (Niacin)**.
- Therefore, **Q = Pellagra (Vitamin B3 deficiency)**.
4. **Analyze R**:
- R is described as affecting "haemoglobin formation in blood."
- This is typically due to a deficiency of **iron**, leading to **anemia**.
- Therefore, **R = Anemia (Iron deficiency)**.
5. **Analyze S**:
- S affects "many metabolic processes of the body and is often characterized by prominent swelling in the neck region."
- This condition is caused by a deficiency of **iodine**, leading to **goiter**.
- Therefore, **S = Goiter (Iodine deficiency)**.
### Summary of Findings:
- **P = Scurvy (Vitamin C deficiency)**
- **Q = Pellagra (Vitamin B3 deficiency)**
- **R = Anemia (Iron deficiency)**
- **S = Goiter (Iodine deficiency)**
### Conclusion:
Based on the analysis, the correct option regarding P, Q, R, and S is that:
- P is caused by Vitamin C deficiency (Scurvy).
- Q is caused by Vitamin B3 deficiency (Pellagra).
- R is caused by Iron deficiency (Anemia).
- S is caused by Iodine deficiency (Goiter).
