Question

Assertion: Formation of $HI$ is a bimolecular reaction
Reason: Two molecules of reactants are involved in this reaction
(a) Both assertion and reason are correct and the reason is the correct explanation for assertion.
(b) Both assertion and reason are correct but the reason is not the correct explanation of assertion.
(c) Assertion is incorrect but the reason is correct
(d) Both assertion and reason are incorrect

Answer 1

Hint: We need to know that bimolecular reaction is the one in which two reactants are involved. The reaction can be reversible or irreversible. The two reactants performing in this reaction can be identical or different, the only condition is the number of reactants which remains fixed, that is two in case of bimolecular reactions.

Complete answer:
When we look at the given statements, the assertion says that formation of $HI$ is a bimolecular reaction. When hydrogen and iodine molecules reactants, they lead to the formation of hydrogen iodide, the reaction can be represented below:
\[{H_2} + {I_2} \to 2HI\]
In the above chemical equation it can be clearly seen that two reactants are involved, that is hydrogen and iodine molecules, thus we can say that the statement given in the assertion is true.
 Now when we look for a second statement that says two molecules of reactants are involved in this reaction: in the formation of hydrogen iodide, two molecules of reactants are involved which is hydrogen and iodine thus the reason statement is also correct.
Thus we can conclude that both assertion and reason are correct for this given question. So, option (A) is correct.

Note:
We need to know that the number of reactants in a chemical reaction tells us whether the reaction is bimolecular, trimolecular or above. The reactants in a given chemical reaction define the molecularity of a reaction. Hydrogen iodide is a diatomic molecule and comes under the class of halides. It is used in organic or inorganic synthesis in which iodine is the first source and behaves as a reducing agent.