Statement – 1: First ionization energy of nitrogen is lower than oxygen.

Statement – 2 : Across the period effective nuclear charge increases.          

Statement – 1 is true, statement – 2 is true, statement – 2 is not a correct explanation for statement - 1

Statement – 1 is true, statement – 2 is true; statement – 2 is a correct explanation for statement - 1

Statement – 1 is true, statement – 2 is false

Statement – 1 is false, statement – 2 is true