Which of the following pairs of elements is most likely to form an ionic compound? a oxygen and fluorine b sodium and aluminum c calcium and chlorine d nitrogen and sulfur

An ionic compound consists of a metal AND a non-metal.

Option A:

Oxygen and fluorine are non-metals.

Option B:

Sodium and aluminium are non-metals.

Option C:

Calcium is a metal and chlorine is a non-metal.

Option D:

Nitrogen and sulfur are non-metals.

Thus, the answer is C.