Electromagnetic radiation is a type of energy that is commonly known as light. Generally, light travels in waves, and all electromagnetic radiation travels at the same speed, which is about 3.0 × 108 ms− 1 through a vacuum.
There are 4 hydrogens on the right side , and 2 hydrogens on the left per molecule of . To get the same number of hydrogens on both sides, the coefficient should be 2.
(Then the number of oxygens will be consistent, since contributes 2 oxygens, and so does .)