Question

Predicate adjective

Not all deserts are sweltering.
The snowy continent of Antarctica is a desert.
Deserts are places with little rainfall.

Answer 1

If the question is in what sentence do you see a predicate adjective, then the correct answer is in the first one - Not all deserts are sweltering, where the word sweltering is a predicate adjective.
A predicate adjective is an adjective that can be found following a verb.