If chlorine gas is bubbled through an aqueous solution of sodium iodide, the result is elemental iodine and aqueous sodium chloride solution. what kind of reaction took place?

NaI + Cl2 → NaCl + I2 You see that there is an imbalance of what you have on each side of the equation. You need to have 2I on the left. So you have to use 2NaI . This gives you 2Na = You have to then make 2NaCl on the right. This has also sorted out the Cl on both sides. 
Balanced equation: 
2NaI + Cl2 → 2NaCl + I2
so this is a Single displacement reaction.When a cation or an anion is exchanged from a compound, this is called as single displacement reaction.

XY + Z → XZ + Y