On complete reaction of ${\mathrm{FeCl}}_3$ with oxalic acid in aqueous solution containing KOH, resulted in the formation of product A. The secondary valency of Fe in the product A is

${\mathrm{FeCl}}_3$ and oxalic acid in an aqueous solution containing KOH completely reacted to produce product A. The product A's secondary valency of Fe is

${\mathrm{FeCl}}_3+3{\mathrm{H}}_2\mathrm{O}+6\mathrm{KOH}\to {\mathrm{K}}_3\left[\mathrm{Fe}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]\left(\mathrm{A}\right)+3\mathrm{KCl}+6{\mathrm{H}}_2\mathrm{O}$
secondary valency is the number of ligands attached to metal ion ${\mathrm{K}}_3\left[\mathrm{Fe}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]$  here C.N = 6
Secondary valency is also 6.
Hence, the product A is${\mathrm{K}}_3\left[\mathrm{Fe}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3\right]$ and its  secondary valency is 6.