$A$ student is given one compound among the following compounds that gives a positive test with Tollen's reagent. The compound is:

$A$ reaction of benzonitrile with one equivalent of $CH_{3}MgBr$ followed by hydrolysis produces a yellow liquid $P$. The compound $P$ will give a positive result for which of the following tests?

Which of the following compounds on reaction with Grignard reagent followed by hydrolysis forms secondary alcohol?

Hex$-4-$en$-2-$ol on treatment with $PCC$ gives $'A'.$ $'A'$ on reaction with sodium hypoiodite gives $'B',$ which on further heating with soda lime gives $'C'.$ The compound $'C'$ is $....... .$

Identify the compound that exhibits tautomerism:

The order of reactivity of phenyl magnesium bromide $(PhMgBr)$ with the following compounds is: