Question

what is organotin or tributyltin (tbt)?
an additive used in highly toxic bottom paint permitted for use on aluminum - hulled boats only.
an additive used in bottom paint that creates an extremely smooth surface that prevents the attachment of fouling organisms.
a form of tin that is more biodegradable and poses little problem in the environment.
a pollutant that makes the eggs of shorebirds soft.

Explanation:

Organotin compounds like tributyltin (TBT) are used as biocides in bottom - paints for boats. They create a smooth surface to prevent the attachment of fouling organisms such as barnacles and algae. TBT is highly toxic and not biodegradable easily and has negative environmental impacts.

Answer:

An additive used in bottom paint that creates an extremely smooth surface that prevents the attachment of fouling organisms.