Assertion (A): ${\mathrm{VF}}_5$ is stable while ${\mathrm{VCl}}_5$ is not.
Reason (R) : Fluorine stabilises the higher oxidation state due to its higher bond enthalpy.
The correct option among the following is

We know that fluorine atom can stabilise the higher oxidation state due to its higher melting point, higher bond enthalpy and small size and that is the reason with vanadium it forms ${\mathrm{VF}}_5$ whereas ${\mathrm{VCl}}_5$ is unstable due to the large size of chlorine atom such that there is no place of accommodation for five big chlorine atoms near the central metal vanadium and because of this stearic hindrance ${\mathrm{VCl}}_5$ does not exist in isolated form while it can exist in dimer form in solid phase.

Hence, assertion and reason both are true and reason is correct explanation of assertion