question_answer 1)

  Ionic radii vary in : (a) inverse proportion to the effective nuclear charge (b) inverse proportion to the square of effective nuclear charge (c) direct proportion to the screening effect (d) direct proportion to the square of screening effect

Answer:

  (a, c) Higher effective nuclear charge is responsible  for more of attraction of electrons and thus, ionic radii decreases. More screening effect means less effective nuclear charge and thus, larger ionic radii.