Water and hydrogen and peroxide (#H_2O_2#) both consists of hydrogen oxygen atoms. Why do they have different chemical and physical properties.?
Law of Multiple Proportions.
The Law of Multiple Proportions states that when 2 elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.
Confusing, but basically the ratio of each element decides the structure and thereby properties so H20 and H202 are very different.