The first step in the reaction is the formation of a carbocation. This occurs when one of the bromine atoms on the meso-stilbene dibromide molecule is displaced by a nucleophile, such as hydroxide ion. This results in the formation of a bromide ion and a carbocation intermediate.

Step 2: Rearrangement of the carbocation

The carbocation intermediate formed in the first step is unstable and quickly rearranges to a more stable carbocation. This rearrangement occurs via a 1,2-shift of a hydrogen atom from the benzylic position to the carbocation center.

Step 3: Formation of the triple bond

In the final step of the reaction, the bromide ion from the first step attacks the carbocation intermediate, resulting in the formation of a triple bond between the two carbon atoms. This results in the formation of diphenylacetylene and hydrogen bromide.

The overall reaction scheme can be represented as follows:

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meso-stilbene dibromide + 2 hydroxide ion → diphenylacetylene + 2 hydrogen bromide + 2 bromide ion

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