If two reactants part in a reaction, then:

Options

A. It can never be of second order
B. It can never be of first order
C. It can never be unimolecular
D. It can never be bimolecular

Answer

To solve the question "If two reactants part in a reaction, then:", we will analyze the implications of having two reactants in a chemical reaction in terms of reaction order and molecularity.

### Step-by-Step Solution:

1. **Understanding Reaction Order**:
- The order of a reaction is determined by the sum of the powers of the concentration terms in the rate law expression. For a reaction involving two reactants A and B, if we assume it is an elementary reaction, the rate law can be expressed as:
\[ \text{Rate} = k[A]^m[B]^n \]
- Here, \(m\) and \(n\) are the stoichiometric coefficients of A and B, respectively. If both A and B participate in the reaction, their coefficients are typically 1 (assuming a simple reaction).

2. **Calculating Total Order**:
- For the reaction \(A + B \rightarrow P\), the total order of the reaction would be:
\[ \text{Total Order} = m + n = 1 + 1 = 2 \]
- This indicates that the reaction is second order overall.

3. **Evaluating First Order**:
- A reaction can be first order if the concentration of one reactant is significantly greater than the other, allowing it to be treated as a constant. For example, if [A] is much larger than [B], we can assume [A] remains constant, and the rate can be expressed as:
\[ \text{Rate} = k' [B] \]
- Here, \(k' = k[A]\) is a new constant. This means the reaction can exhibit first-order kinetics with respect to B.

4. **Molecularity Consideration**:
- Molecularity refers to the number of reactant species involved in an elementary reaction. Since we have two reactants (A and B), the molecularity is bimolecular.
- A reaction cannot be unimolecular if it involves two reactants because unimolecular reactions involve only one species undergoing a change.

5. **Conclusion**:
- Therefore, if two reactants are participating in a reaction, it can be concluded that:
- It can be of second order (as shown).
- It can potentially exhibit first-order behavior under certain conditions.
- It cannot be unimolecular because there are two reactants involved.

### Final Answer:
If two reactants part in a reaction, then:
- It can be of second order.
- It can potentially exhibit first-order behavior under specific conditions.
- It cannot be unimolecular.