The correct answer is: I, III.
Xenobiotics are chemicals that are foreign to an organism or ecosystem. They can be natural or synthetic, and they can be found in the air, water, soil, and food. Some xenobiotics are biodegradable, meaning that they can be broken down by microorganisms. Others are non-biodegradable, meaning that they can persist in the environment for long periods of time. Xenobiotics can pose a threat to the environment because they can accumulate in organisms and disrupt their normal functioning. They can also cause problems for ecosystems by altering the balance of organisms.
Option I is correct because some xenobiotics are biodegradable. This means that they can be broken down by microorganisms and their components can be reused by other organisms. Biodegradable xenobiotics are less likely to pose a threat to the environment than non-biodegradable xenobiotics.
Option II is incorrect because some xenobiotics are non-biodegradable. This means that they cannot be broken down by microorganisms and their components will remain in the environment for long periods of time. Non-biodegradable xenobiotics are more likely to pose a threat to the environment than biodegradable xenobiotics.
Option III is correct because xenobiotics can pose a threat to the environment. They can accumulate in organisms and disrupt their normal functioning. They can also cause problems for ecosystems by altering the balance of organisms.
Option IV is incorrect because xenobiotics are not always environment friendly. Some xenobiotics can pose a threat to the environment.