The set of species having only fractional bond order values is

Step-by-step solution

Bond order ( BO )= 1 2 (number of electron in bonding MO's - number of electron in anti-bonding MO ^ s ) C ₂²⁻: Total number of electrons =6+6+2=14 Electronic configuration (1 s^2 ), ^* (1 s^2 ), (2 s^2 ), ^* (2 s^2 ), 2 p_x^2= 2 p_y^2, 2 p_z^2 BO = 1 2 (10-4)= 1 2 6=3 N _ 2 : Total number of electrons =7+7=14 (1 s^2 ), ^* (1 s^2 ), (2 s^2 ), ^* (2 s^2 ), 2 p_x^2= 2 p_y^2, 2 p_z^2 BO = 1 2 (10-4)= 6 2 =3 O ₂²⁻: Total number of electron =8+8+2=18 array r (1 s^2 ), ^* (1 s^2 ), (2 s^2 ), ^* (2 s^2 ), 2 p_z^2, 2 p_x^2