22. Cerium(IV) ion is a strong oxidizing agent that accepts one electron to produce cerium(III) ion. A solution containing an unknown concentration of $Sn^{2+}$ ions was titrated with a solution containing $Ce^{4+}$ ions, which oxidize the $Sn^{2+}$ ions to $Sn^{4+}$ ions. In one titration $1.00\ \mathrm{L}$ of the unknown solution required $46.45\ \mathrm{mL}$ of a $0.1050\ \mathrm{M}\ Ce^{4+}$ solution to reach the stoichiometric point. $$ a\ Ce^{4+}(aq) + b\ Sn^{2+}(aq) \longrightarrow c\ Ce^{3+}(aq) + d\ Sn^{4+}(aq) $$ What is the closest concentration of $Sn^{2+}$ ions in the unknown solution?
(A) $2.4 \times 10^{-3}$
(B) $2.4 \times 10^{-2}$
(C) $2.7 \times 10^{-3}$
(D) $2.7 \times 10^{-2}$
(E) $3.0 \times 10^{-3}$