Here's why:

* Sodium chloride (NaCl) is a compound formed from the ionic bond between one sodium atom (Na) and one chlorine atom (Cl).

* Mole ratio refers to the ratio of moles of each element in a compound.

* One mole of sodium chloride contains one mole of sodium atoms and one mole of chlorine atoms.

Therefore, the mole ratio of sodium to chlorine in sodium chloride is 1:1.