The correct answer is option 'C', the Law of Reciprocal Proportions. Let's understand this in detail:

Law of Reciprocal Proportions:
The Law of Reciprocal Proportions is a principle in chemistry that states that when two elements combine separately with a fixed mass of a third element, the ratios in which they combine with each other will be either the same or simple multiple of each other.

Explanation:
Chemical equations represent the chemical reactions that occur between different substances. They are written to show the reactants and products involved in a reaction. These equations follow certain laws and principles that govern the behavior of matter. One such principle is the Law of Reciprocal Proportions.

Law of Constant Proportion:
The Law of Constant Proportion states that a chemical compound always contains the same elements in the same proportions by mass. This means that the ratio of the masses of the elements in a compound is always constant.

Law of Multiple Proportions:
The Law of Multiple Proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.

Chemical Equations and the Law of Reciprocal Proportions:
Chemical equations can be written on the basis of the Law of Reciprocal Proportions because this law allows us to determine the ratios in which elements combine with each other. When we write a chemical equation, we need to balance it by ensuring that the number of atoms of each element on both sides of the equation is the same.

The Law of Reciprocal Proportions helps us determine these ratios and ultimately balance the equation. It allows us to understand the stoichiometry of the reaction, which refers to the quantitative relationships between the reactants and products in a chemical reaction.

Conclusion:
In conclusion, chemical equations can be written on the basis of the Law of Reciprocal Proportions. This law helps us determine the ratios in which elements combine with each other and allows us to balance chemical equations by ensuring that the number of atoms of each element is the same on both sides of the equation. By understanding the principles and laws that govern chemical reactions, we can accurately represent and predict the behavior of matter.