2. Four cities each send 3 political advisors to participate in $k$ group inspection activities (each advisor can participate in several groups), with the rules: (1) advisors from the same city are not in the same group; (2) any two advisors from different cities exactly participate in one activity together. Then the minimum value of $k$ is $\qquad$ .
2.9 Group.

First, consider the CPPCC members from two cities, Jia and Yi. Let the members from Jia city be $A_{1}, A_{2}, A_{3}$, and the members from Yi city be $B_{1}, B_{2}, B_{3}$. They can form 9 pairs: $A_{1} B_{1}, A_{1} B_{2}, A_{1} B_{3}, A_{2} B_{1}, A_{2} B_{2}, A_{2} B_{3}$, $A_{3} B_{1}, A_{3} B_{2}, A_{3} B_{3}$. According to the problem, the number of groups $k$ is no less than 9. To minimize the number of groups, the number of people in each group should be as large as possible (up to 4 people), and the following nine groups can be arranged to meet the requirements:
$$
\begin{array}{ll}
\left(A_{1}, B_{1}, C_{1}, D_{1}\right) & \left(A_{1}, B_{2}, C_{2}, D_{2}\right) \\
\left(A_{1}, B_{3}, C_{3}, D_{3}\right) & \left(A_{2}, B_{1}, C_{2}, D_{3}\right) \\
\left(A_{2}, B_{2}, C_{3}, D_{1}\right) & \left(A_{2}, B_{3}, C_{1}, D_{2}\right) \\
\left(A_{3}, B_{1}, C_{3}, D_{2}\right) & \left(A_{3}, B_{2}, C_{1}, D_{3}\right) \\
\left(A_{3}, B_{3}, C_{2}, D_{1}\right) &
\end{array}
$$