Taking into account the stability of various carbocations and the rules governing mechanisms of carbocation rearrangements,which reaction is most likely to occur during the given reaction?

Which one of the following carbocations is the most stable?

The correct order of stability of the following carbocations is:

State True or False for the following statements:
$(i)$ $\mathop{C}\limits^{+}H_3$ and $CH_3\mathop{C}\limits^{+}H_2$ both are primary carbocations.
$(ii)$ $(CH_3)_3\mathop{C}\limits^{+}$ is a tertiary carbocation and all carbons are $sp^3$ hybridized.
$(iii)$ $\mathop{C}\limits^{+}H_3$ is trigonal planar.
$(iv)$ $CH_4$ is not trigonal planar.

Which of the following is the most stable carbocation?

Which of the following is the most stable carbanion?