Statement I : Sodium reacts with excess O2 to form Na2O2 where as 'K' reacts to form KO2Statement II : 'K' is more reactive than Na

As the size of cation increases polarising power of cation decreases,the ability of oxide ion and peroxide ion  to loose electron increases,hence large size ion forms superoxide.With increase in size down the group ionization energy decrease,reactivity increases.