The correct answer is option 'C': Lipo protein.

The viral envelope is the outermost layer of a virus that surrounds the protein coat, also known as the capsid. It is a unique feature of some viruses, particularly enveloped viruses. The viral envelope is derived from the host cell's plasma membrane or other cellular membranes, and it plays a crucial role in the virus's ability to infect and replicate within host cells.

The composition of the viral envelope is primarily lipid-protein complexes, known as lipo proteins. These lipo proteins are formed by the combination of viral proteins and host cell lipids. The viral proteins embedded in the lipid bilayer are responsible for various functions, including viral attachment, fusion with host cell membranes, and evasion of the host immune response.

Here is a breakdown of the composition of the viral envelope:

1. Lipids:
- The viral envelope is primarily composed of lipids, including phospholipids, cholesterol, and glycolipids.
- Phospholipids are the main building blocks of the lipid bilayer, forming a double layer of lipids with hydrophilic heads facing outward and hydrophobic tails facing inward.
- Cholesterol molecules are interspersed within the lipid bilayer, providing stability and fluidity to the envelope.
- Glycolipids are lipids with attached carbohydrate chains, which are involved in viral attachment to host cells and immune evasion.

2. Proteins:
- The viral envelope contains viral proteins that are embedded within the lipid bilayer.
- These proteins serve various functions, including viral attachment to host cell receptors, fusion with host cell membranes, and modulation of the host immune response.
- The viral envelope proteins are often glycosylated, meaning they have carbohydrate chains attached, which helps in immune evasion and recognition.

3. Lipo proteins:
- Lipo proteins are complexes of viral proteins and host cell lipids.
- They are formed during the viral replication cycle when the virus buds from the host cell membrane or other cellular membranes.
- The viral proteins incorporated into the lipo proteins determine the specific functions of the viral envelope, such as viral tropism (cellular targeting) and fusion with host cell membranes.

In conclusion, the viral envelope is composed of lipo proteins, which are lipid-protein complexes formed by the combination of viral proteins and host cell lipids. These lipo proteins play essential roles in viral attachment, fusion, and immune evasion.