Final answer:
The least serious value for the Availability metric in CVSS2#AV:N/AC:L/Au:N/C:P:/I:N/A:N indicates that a successful exploitation of the vulnerability would have no availability impact.
Step-by-step explanation:
In CVSS2#AV:N/AC:L/Au:N/C:P:/I:N/A:N, the value 'A:N' indicates that a successful exploitation of this vulnerability would have no availability impact. This means that the vulnerability does not affect the availability of the target system. The 'A' in the CVSS2 formula stands for Availability, and 'N' represents None. Therefore, this is the least serious value for the Availability metric.