How many grams of Cl2 are consumed to produce 12.0 g of KCl?

The reaction is:

Cl2 + 2 KBr - -> 2 KCl + Br2

Moles of KCl is

n = m / M = 12 / 74 = 0.16 mol

As, twice the moles of KCl is producing from 1 mol of chlorine

mole of Cl2 = 0.16 / 2 = 0.08 mol

Mass of Cl2

m / 70 = 0.08 = 5.6 g

Hence, 5.6 g mol Cl2 consumed to produce KCl