Answer: option B - 2 K + MgBr2 = 2 KBr + Mg
Explanation:
2K + MgBr2 --> 2 KBr + Mg
On Left side: 2moles of Potassium (K) reacts with 1 mole of MgBr2
On Right side: 2 moles of KBr and 1 mole of Mg.
You will observe that the coefficient of each element on left side and Right side is balanced in option B, unlike other options.
So, option B is the answer.