Which carbocation is the most stabilized?

Which of the following compounds is not resonance stabilized?

Which is the correct structure of trans-$2$-hexenal?

Amongst the following amino acids,the $(R)$-enantiomer is represented by:

Which of the given statement(s) about $N$, $O$, $P$ and $Q$ with respect to $M$ is (are) correct?
$(A)$ $M$ and $N$ are non-mirror image stereoisomers
$(B)$ $M$ and $O$ are identical
$(C)$ $M$ and $P$ are enantiomers
$(D)$ $M$ and $Q$ are identical

Which of the following contains a plane of symmetry?