Which one of the lanthanoids given below is the most stable in divalent form?

Kindly consider the following 

Magnetic moment (in BM) of Cu²⁺ ion is

K₂Cr₂O₇ + H₂O₂ + H₂SO_{4 $\underset{conditions}{\overset{ether cold}{\to }}$} <!-- [if gte mso 9]><xml> </xml><![endif]-->compound 'X' X is a chromium compound, what is the oxidation state of chromium in compound 'X'.

Alkaline KMnO oxidises lodide to a particular product (A). Determine the oxidation state of lodine in compound (A).

Which of the following pair will be formed by the decomposition of KMnO₄?