Refer to the given dichotomous key and select the correct option.
I. (a) It is categorised as energy giving food . - Go to II
(b) It is categorised as protective food. - Go to III
II. (a) It is soluble in water . - P
(b) It is insoluble in water. - Q
III. (a) It is needed for clotting of blood . - R
(b) It helps in formation of haemoglobin. - S

Options

A. Q could be glucose which is instant source of energy.
B. Deficiency of S causes anaemia characterised by pale body colour, body fatigue, etc.
C. Deficiency of R causes osteoporosis in adults while deficiency of S causes goitre in adults.
D. P could be butter which gives an oily patch on the filter paper.

Explanation

To solve the question using the provided dichotomous key, we will follow the steps outlined in the key to identify the correct food category and its characteristics.

### Step-by-Step Solution:

1. **Identify the Food Category**:
- The first part of the key states:
- (a) It is categorized as energy giving food.
- (b) It is categorized as protective food.
- We need to determine if the food in question is energy-giving or protective.

2. **Follow the Path Based on the Food Category**:
- If the food is categorized as energy-giving (option I (a)), we go to II.
- If it is categorized as protective food (option I (b)), we go to III.

3. **Analyze Energy-Giving Food**:
- In section II:
- (a) It is soluble in water. - This leads to option P.
- (b) It is insoluble in water. - This leads to option Q.
- Here, we need to determine if the energy-giving food is soluble or insoluble in water.

4. **Identify Protective Food**:
- In section III:
- (a) It is needed for clotting of blood. - This leads to option R.
- (b) It helps in the formation of hemoglobin. - This leads to option S.
- Here, we need to determine if the protective food is related to blood clotting or hemoglobin formation.

5. **Determine the Specific Food Item**:
- For energy-giving foods, carbohydrates are typically the source.
- If it is soluble in water, it could be glucose (option P).
- If it is insoluble in water, it could be starch (option Q).
- For protective foods:
- Vitamin K is essential for blood clotting (option R).
- Iron is essential for hemoglobin formation (option S).

6. **Conclusion**:
- Based on the analysis:
- If the food is energy-giving and soluble in water, it is glucose (P).
- If it is protective and helps in clotting, it is Vitamin K (R).
- If it helps in hemoglobin formation, it is Iron (S).
- The correct option based on the dichotomous key is option 2.