Dialkyl ethers can react with halogen acids (such as hydrogen chloride or hydrogen bromide) to form alkyl halides. In this reaction, one molecule of dialkyl ether reacts with one molecule of halogen acid to produce two molecules of alkyl halides. Therefore, the correct answer is option B, which states that one molecule of dialkyl ether produces two molecules of alkyl halides with an excess of halogen acid.

Explanation:

1. Reaction between dialkyl ether and halogen acid:
When a dialkyl ether reacts with a halogen acid, the ether oxygen (O) atom is replaced by a halogen (X) atom. This reaction is known as the Williamson ether synthesis.

2. General reaction equation:
The general reaction equation for the reaction between a dialkyl ether and a halogen acid can be represented as:
R-O-R' + HX → R-X + R'-OH
where R and R' represent alkyl groups and X represents a halogen atom (Cl, Br, I).

3. Stoichiometry of the reaction:
The stoichiometry of the reaction shows that one molecule of dialkyl ether reacts with one molecule of halogen acid to produce two molecules of alkyl halides. This can be understood by examining the reaction equation.

4. Example:
For example, let's consider the reaction between ethyl methyl ether (CH3OCH2CH3) and hydrogen chloride (HCl). The reaction can be represented as:
CH3OCH2CH3 + HCl → CH3Cl + CH3CH2OH

In this example, one molecule of ethyl methyl ether reacts with one molecule of hydrogen chloride to produce two molecules of alkyl halides: methyl chloride (CH3Cl) and ethanol (CH3CH2OH).

5. Excess of halogen acid:
The question specifies that there is an excess of halogen acid. This means that there are more than enough molecules of halogen acid available for the reaction. Therefore, all the molecules of dialkyl ether can react with the halogen acid, resulting in the formation of alkyl halides.

In summary, one molecule of dialkyl ether reacts with one molecule of halogen acid to produce two molecules of alkyl halides. With an excess of halogen acid, all the molecules of dialkyl ether can react, resulting in the formation of a larger number of alkyl halide molecules.