Which of the following will act as the best oxidizing agent?

Write the chemical reactions of lanthanoids $(Ln)$ with the following:
$(1)$ With acid:
$2Ln + 6HCl \rightarrow 2LnCl_3 + 3H_2$
$(2)$ With halogens ($X_2$,where $X = F, Cl, Br, I$):
$2Ln + 3X_2 \rightarrow 2LnX_3$

$Cu^{2+}$ ions will be reduced to $Cu^{+}$ ions by the addition of an aqueous solution of

When an excess of $KI$ is added to a $CuSO_4$ solution and then $Na_2S_2O_3$ is added to the mixture,which of the following statements is incorrect?

In which of the following, ions are correctly arranged in the increasing order of oxidizing power?

Identify the correct statement.