= Solution
The conserved total molecule amount fixes the final common <concentration>:
$$
c_\infty=\frac{V_cc_c(0)+V_nc_n(0)}{V_c+V_n}.
$$
Solve $c_c-c_n=\Delta c(t)$ together with $V_cc_c+V_nc_n=(V_c+V_n)c_\infty$ to obtain
$$
\boxed{c_c(t)=c_\infty+\frac{V_n}{V_c+V_n}\Delta c(t)},\qquad
\boxed{c_n(t)=c_\infty-\frac{V_c}{V_c+V_n}\Delta c(t)}.
$$
Substituting the decaying <concentration> difference from part (d) supplies both explicit time dependences. The <concentrations> approach the volume-weighted initial average, which need not be the arithmetic average if the compartment volumes differ.
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