Which of the following is a least stable carbocation?

• A

  $\mathrm{CH}_3-\stackrel{\oplus}{\mathrm{C}} \mathrm{H}_2$
• Correct answer
  B

  $\mathrm{CH}_2=\stackrel{\oplus}{\mathrm{C}} \mathrm{H}$
• C

  $\mathrm{CH}_2=\mathrm{CH}-\stackrel{\oplus}{\mathrm{C}} \mathrm{H}_2$
• D

  $\mathrm{C}_6 \mathrm{H}_5-\stackrel{\oplus}{\mathrm{C}} \mathrm{H}_2$

Hence, the correct answer is option: 'B'.