The correct options are
A Lithium and oxygen
B Sodium and flourine
D Sodium and oxygen
An ionic bond is formed by the transferring of electrons from a metal to a non-metal. For ionic bond formation, the difference in the electronegativities of the constituent atoms is more than 1.9.
Among the given elements difference of electronegativity are as follow:
∙ Phosphorous and fluorine = 3.98 - 2.19 = 1.79
∙ Lithium and oxygen = 3.44 - 0.98 = 2.46
∙ Sodium and oxygen = 3.44 - 0.93 = 2.51
∙ Sodium and flourine = 3.98 - 0.93= 3.05
Hence, lithium and oxygen, sodium and oxygen, sodium and fluorine form ionic bonds.
While, phosphorous and fluorine form a covalent bond, because
the electronegativity difference between phosphorous and fluorine is 1.79, which is less than 1.9.