The correct answer is option 3, which states that viruses can synthesize their own food through photosynthesis.

Option 1 states that viruses need living cells to reproduce, which is true. Viruses cannot reproduce on their own and rely on host cells to replicate their genetic material and produce more viruses.

Option 2 states that all viruses are parasites, and this is generally true. Viruses are considered obligate intracellular parasites because they require a host cell to complete their life cycle. They hijack the host cell`s machinery to replicate and produce more viruses.

Option 4 states that viruses are similar to chemical substances outside the host. This is also true as viruses, when outside the host, exist as inert particles called virions. Virions are not considered living entities as they lack the ability to perform metabolic functions on their own. They behave more like chemical substances until they infect a host cell.

In conclusion, option 3 is the correct answer because viruses cannot synthesize their own food through photosynthesis. They depend entirely on host cells for replication and survival.