Exoskeleton is absent in.
(i) fishes `" "` (ii) frog
(iii) rabbit `" "` (iv) food .

Answer

To determine which option does not have an exoskeleton, we need to analyze each option provided:

1. **Fishes**: Fishes typically have scales that form an exoskeleton. These scales provide protection and are considered a type of exoskeleton.

2. **Frog**: Frogs have a skin that acts as an exoskeleton. Their skin protects them and also plays a role in respiration.

3. **Rabbit**: Rabbits have fur and skin that can be considered a protective layer, which can also be classified as an exoskeleton.

4. **Food**: Food does not have an exoskeleton. It is organic matter that is consumed and does not possess any structural protective layer like an exoskeleton.

Based on this analysis, the option that is absent of an exoskeleton is:

**Answer: (iv) food**

### Step-by-Step Solution:
1. **Identify the characteristics of exoskeleton**: Understand that an exoskeleton is a hard protective outer structure found in some animals.

2. **Analyze each option**:
- **Fishes**: Recognize that they have scales as an exoskeleton.
- **Frog**: Note that their skin serves as an exoskeleton.
- **Rabbit**: Acknowledge that their fur and skin provide a protective layer.
- **Food**: Realize that food is not an organism and does not have an exoskeleton.

3. **Conclude**: Determine which option does not fit the criteria of having an exoskeleton.