Electrostatic field lines must satisfy specific properties: (1) They start from positive charges and end on negative charges. (2) They do not form closed loops. (3) They never cross each other. (4) They are always normal (perpendicular) to the surface of a conductor. Any representation violating these rules (e.g., forming loops, crossing, or not being normal to conductors) is incorrect. The curve labeled '4' is identified as the correct representation satisfying these conditions. (See NCERT Physics Class 12, Section 1.8 and 1.9).