Final answer:
The number that should be placed in front of KBr to balance the chemical equation Br2 + 2KI → KBr + I2 is 2, which ensures that the potassium and bromine atoms are balanced on both sides of the equation.
Step-by-step explanation:
To determine what number should be placed in front of KBr to balance the chemical equation Br2 + 2KI → KBr + I2, we must ensure that there are equal numbers of each type of atom on both the reactants and products side of the equation.
Looking at the iodine atoms, we have 2 iodine atoms on the reactant side (from 2KI), and two on the product side (from I2). The potassium atoms from 2KI also require 2 KBr molecules to balance them, as there are 2 potassium atoms present.
Thus, the balanced equation should look like: Br2 + 2KI → 2KBr + I2. This means that the number which should be placed in front of KBr is 2. So, the correct answer is A. 2.