${\mathrm{PCl}}_5$ is well known but ${\mathrm{NCl}}_5$ is not.Because,

• Correct answer
  A

  $\mathrm{N}$ - does not have vacant $\mathrm{d}$-orbital
• B

  $\mathrm{P}$ - does not have $2\mathrm{d}$ orbitals
• C

  Back bonding in ${\mathrm{NCl}}_5$ is not possible
• D

  $\mathrm{N}$ atom is more electronegative so does not forms $5$ bonds

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