Dependance of rate on concentration is expressed by

Options

A. Rate law
B. order of reaction
C. Molecularity
D. Law of mass action

Explanation

To answer the question "Dependence of rate on concentration is expressed by," we need to analyze the options provided and determine which one accurately describes this relationship.

### Step-by-Step Solution:

1. **Understanding Rate Law**:
- The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants. It is generally written as:
\[ \text{Rate} = k [A]^x [B]^y \]
where \( k \) is the rate constant, \([A]\) and \([B]\) are the concentrations of the reactants, and \( x \) and \( y \) are the orders of the reaction with respect to each reactant.

2. **Identifying the Order of Reaction**:
- The order of a reaction is the sum of the powers to which the concentrations are raised in the rate law. It indicates how sensitive the rate of the reaction is to changes in the concentration of the reactants. However, it does not directly express the dependence of the rate on concentration.

3. **Understanding Molecularity**:
- Molecularity refers to the number of reactant molecules involved in an elementary step of a reaction. While it provides insight into the reaction mechanism, it does not describe how the rate depends on concentration.

4. **Considering the Law of Mass Action**:
- The law of mass action relates the concentrations of reactants and products at equilibrium but does not specifically address the rate of reaction. It is more about the extent of a reaction rather than the rate.

5. **Conclusion**:
- After analyzing all the options, the correct expression for the dependence of rate on concentration is the **Rate Law**. Therefore, the answer is:
\[ \text{Rate Law} \]

### Final Answer:
The dependence of rate on concentration is expressed by **Rate Law**.

---