We have to balance this equation:
__ K + __ Br₂ ----> __ KBr
The first step to balance any equation we have to find the quantity of each element that we have on each side of the equation.
__ K + __ Br₂ ----> __ KBr
Br: 2 Br: 1
K: 1 K: 1
According to the equation we have two atoms of Br on the left and only one atom of Br on the right. If we want to balance the atoms of Br we have to change the coefficient in front of KBr and write a 2 there. Let's see what happens when we change it.
__ K + __ Br₂ ----> 2 KBr
Br: 2 Br: 2
K: 1 K: 2
Changing that coefficient we balanced the Br, but we unbalanced the K. Now we have two atoms of K on the right and one atom of K on the left. To balance it we have to write a two in front of K.
2 K + __ Br₂ ----> 2 KBr
Br: 2 Br: 2
K: 2 K: 2
Finally the equation is balanced. So the answer to our problem is:
2 K + Br₂ ----> 2 KBr