The Best way to check whether $A \rightarrow B$ is a valid implication or Not, Just Try to make $A$ true and $B$ false... If you can somehow do it then it means Invalid implication. And If you can't make $A$ true and $B$ false simultaneously then Valid implication. It's because, we know $A \rightarrow B$ is False If and Only if $A$ is True and $B$ is False.
1. $(P \Leftrightarrow Q) \rightarrow (P \rightarrow Q)$ Is Valid implication i.e is Tautology.
2. $(P \wedge Q) \rightarrow (P \Leftrightarrow Q)$ Is Valid Implication i.e. is Tautology.
3. $(P \Leftrightarrow Q) \rightarrow (P \rightarrow Q')$ Is NOT valid implication i.e. Not tautology.
4. $(P \Leftrightarrow Q') \rightarrow (P \rightarrow Q)$ Is NOT valid implication i.e. Not tautology.