Excess of KI reacts with ${\mathrm{CuSO}}_4$ solution and then ${\mathrm{Na}}_S{\mathrm{S}}_2{\mathrm{O}}_3$ solution is added to it. Which of the statements is incorrect for this reaction?

Potassium iodide and copper sulphate react to produce cuprous iodide and iodine.
$2{\mathrm{CuSO}}_4+4\mathrm{KI}\to {\mathrm{Cu}}_2{\mathrm{I}}_2+{\mathrm{I}}_2+2{\mathrm{K}}_2{\mathrm{SO}}_4;$

${\mathrm{CuI}}_2$ does not, therefore, result from this reaction.
As a result, option B is erroneous and option A is the proper choice.
To create sodium tetrathionate, sodium thiosulphate is titrated with the freed iodine.
$2{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3+{\mathrm{I}}_2\to {\mathrm{Na}}_2{\mathrm{S}}_4{\mathrm{O}}_6+2\mathrm{NaI}$
Iodine is oxidised whereas sodium thiosulfate is decreased.