Examine the following unbalanced chemical equation: CO2 + C → CO. Which of the following is the correctly balanced form of this equation?

In order to balance this, you have to count each element where the elements in the reactants side and the product side should have equal number of molecules. The balanced reaction is as follows:

CO2 + C → 2CO

There are 2 C atoms for each side and 2 atoms of O at each side. Therefore, it is balanced.