A sample of an arsenic compound weighing 0.3245 g was dissolved and all the arsenic converted to arsenic in the +3 oxidation state.

A sample of an arsenic compound weighing 0.3245 g was dissolved and all the arsenic converted to arsenic in the +3 oxidation state.  A 0.0250 M solution of a reagent, R, was added which oxidized the arsenic to the +5 oxidation state.  R contains a metal in the +4 state that was reduced to the +2 state.  If it took 15.64 mL of the solution of R to exactly react with the arsenic, what is the percentage of arsenic in the sample?

a) 1.107      b) 1.694      c) 18.05      d) 22.57      e) 9.027