Question

FeI3 does not exist while FeCl3 exists. Why?

Answer 1

I- is much larger in size, so has higher tendency to lose electron, and hence is a good reducing agent. I- reduces Fe3+ to Fe2+ and itself gets oxidised to I2, hence FeI3 is unstable.
2FeI3 ———> 2FeI2 + I2

Meanwhile, Cl- is smaller in size and has high tendency to gain electron. So, it being an oxidising agent oxidises Fe2+ to Fe3+, which favours formation of FeCl3 and makes it stable.