Question

which is the formula for a binary ionic compound composed of iodine and sodium?
a ina
b nai
c iodine and sodium do not form a binary ionic compound.
d either ina or nai is acceptable.

Explanation:

To determine the formula of a binary ionic compound, we follow the rule that the cation (metal) is written first, followed by the anion (non - metal). Sodium (Na) is a metal and forms the $Na^+$ cation. Iodine (I) is a non - metal and forms the $I^-$ anion. In the formula of an ionic compound, we write the symbol of the cation first and then the symbol of the anion. So, the formula should be NaI (sodium iodide). Option a is incorrect because it writes the anion first and the cation second. Option c is incorrect as sodium and iodine do form a binary ionic compound (sodium iodide). Option d is incorrect because the order of writing the cation and anion in the formula of an ionic compound is not arbitrary; the cation must come first.

Answer:

b. NaI