Which two atoms form an ionic bond?
a. two sodium atoms
b. two oxygen atoms
c. sodium and bromine
d. fluorine and chlorine

Sodium and bromine

Explanation:

Ionic bond is a type of chemical bond and binds the chemical molecules together.  Ionic bond is formed by the transfer of electrons from an electropositive element ( metal) to the electronegative element (non metal).

Sodium is an electropositive element and contains one positive charge. Bromine is an electronegative element with a single negative charge over it. Sodium gives the electron to bromine and results in the formation of ionic bond.

Thus, the correct answer is option (C).