In an aqueous solution of KCl the transport number of $\mathrm{K}{}^{+}$ is $0.49$. The transport number of $\mathrm{Cl}{}^{-}$ in this solution is

The transport number is the fraction of total current carried by an ion, so for a solution of a single electrolyte $t_{+}+t_{-}=1$. $t(\mathrm{Cl}{}^{-})=1-0.49=0.51$. The slightly larger value for $\mathrm{Cl}{}^{-}$ reflects its slightly higher ionic conductivity ($76.3$ vs $73.5\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$).