Accounting from the following : 2nd period elements show anomalous behaviour

Name the element showing anomalous behaviour in group 2.

Two students were analysing the electronic configurations of the first 30 elements of the Periodic Table as part of an assignment. They found that two elements showed difference from other twenty eight elements. Why they show this anomalous behavior?

Account for the following: H_2O_2 is a bleaching agent.

Accounting from the following : Ionization enthalpy of Nitrogen is greater than that of Oxygen.

Account for the following: CO_2 is linear but SO_2 is angular.

Account for the following:- NO_2 dimerises to N_2O_4 .

Account for the following:-Transition elements form a number of interstitial compounds.

Give reason for anomalous behaviour in group 2.