Assume that 7.2 L of I2 are produced at STP according to the following balanced equation:

2KI+Cl - 2KCl+ I2
How many grams of KI (MOLAR MASS=166.002G/MOL) reacted

You have the balanced equation.

mol I2 = L/22.4 = ?

Use the coefficients in the balanced equation to convert mols I2 to mols KI.

Convert mols kI to grams. g = mols x molar mass.