The number of following factors which affect the percent covalent character of the ionic bond is______
A) Polarising power of cation
B) Extent of distortion of anion
C) Polarisability of the anion
D) Polarising power of anion

Fajans' Rules

Evaluation of the Given Factors:

• A) Polarising power of cation 
  Yes. A smaller, highly charged cation has greater pulling strength (polarizing power) to deform the anion, increasing covalent character.
  $$\text{}$$
• B) Extent of distortion of anion
  Yes. The "extent of distortion" is the literal visual representation of polarization itself. More distortion directly translates to higher covalent character sharing.
  $$\text{}$$
• C) Polarisability of the anion 
  Yes. Large anions with loosely held outer shells are easily deformed (highly polarizable), which favors covalent character formation.
  $$\text{}$$
• D) Polarising power of anion 

  No. The anion undergoes polarization; it is not the one doing the active squeezing or pulling. Hence, the "polarizing power of an anion" is an incorrect/irrelevant parameter here.

Summary:

Factors A, B, and C all validly influence the overall percent covalent character, whereas D does not. Therefore, there are exactly 3 correct factors.