If $P \Rightarrow \left( {q \vee r} \right)$ is false, then the truth values of $p, q, r$ are respectively

Which of the following Boolean expression is a tautology ?

$(p \to q) \leftrightarrow (q\ \vee  \sim p)$ is 

Negation of the compound proposition : If the examination is difficult, then I shall pass if I study hard

Consider the statement : "For an integer $n$, if $n ^{3}-1$ is even, then $n$ is odd." The contrapositive statement of this statement is

The contrapositive of the statement "If you will work, you will earn money" is ..... .