There are four alcohols P, Q, R and S which have 3, 2, 1 and zero alpha hydrogen atom(s) respectively. Which one of the following will give an alkene when heated with copper

When primary or a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and an aldehyde or a ketone is formed while tertiary alcohols undergo dehydration and forms alkene.

S is a tertiary alcohol because it has zero alpha hydrogen and forms alkene when heated with Cu.