Which one of the following equations is not balanced?
6h2o + 6co2 > c6h12o6 + 6o2
c7h16 + 11o2 > 7co2 + 8h2o
pcl2 + 4h2o > h3po4 + 5hcl
fe3o4 + 4h2 > 3fe + 4h2o

The key in the balancing of chemical reaction is to make sure that you got the exact chemical formula of the substance that is reacting and the yielded product. After getting the formula, identify first the hardest element/atom to be balanced such as Na, Zn, Cl, C, O, etc. Then proceed to the easier ones such as O, H. Make sure to note the atoms present in the molecule of the substance. Among the three equations, PCl2 + 4H2O --->H3PO4 + 5HCL is not balanced. The hardest element here is the Cl. Observe that there are 5Cls in the product side so you must add 5 to the PCl2. However, there are only 2Cl atoms and it needs 3 to balance the equation. Also, there is no P in the product side. This equation is invalid.