Contrapositive and Contradiction · Medium problem

"If $3 \mid n^2$, then $3 \mid n$" and "if $3 \mid n$, then $3 \mid n^2$"

"If $3 \mid n^2$, then $3 \mid n$" and "if $3 \nmid n$, then $3 \nmid n^2$"

"If $3 \mid n^2$, then $3 \mid n$" and "if $3 \nmid n^2$, then $3 \nmid n$"

"If $3 \mid n^2$, then $3 \mid n$" and "if $3 \nmid n$, then $3 \mid n^2$"