To determine which of the given options is a polyhydrocarbon, we first need to understand what a polyhydrocarbon is. A polyhydrocarbon is a polymer made up of hydrocarbon monomers, which consist solely of carbon (C) and hydrogen (H) atoms.
### Step-by-Step Solution:
1. **Define Polyhydrocarbon**:
- A polyhydrocarbon is a polymer formed from hydrocarbon monomers, meaning it contains only carbon and hydrogen atoms.
2. **Analyze Each Option**:
- **Starch**:
- The monomer unit of starch is glucose (C6H12O6), which contains carbon, hydrogen, and oxygen. Therefore, starch is not a polyhydrocarbon.
- **Natural Rubber**:
- The monomer unit of natural rubber is 2-methylbuta-1,3-diene, which has the structure CH2=CH-CH(CH3)-CH=CH2. This structure contains only carbon and hydrogen. Hence, natural rubber qualifies as a polyhydrocarbon.
- **Casein**:
- Casein is a protein found in milk, with a complex structure that includes carbon, hydrogen, nitrogen, oxygen, and phosphorus (C81H125N22O39P). Thus, it is not a polyhydrocarbon.
- **Perylene**:
- Perylene is formed from monomers like ethylene glycol and terephthalic acid, both of which contain oxygen in addition to carbon and hydrogen. Therefore, perylene is not a polyhydrocarbon.
3. **Conclusion**:
- Among the options analyzed, only natural rubber consists solely of carbon and hydrogen, making it the only polyhydrocarbon. Therefore, the correct answer is **natural rubber**.
### Final Answer:
- The polyhydrocarbon among the options is **Natural Rubber**.
