What is Q?

\(R-H\)

The correct answer is option 4. \(R-H\).

The reaction involves the preparation of an organometallic compound called a Grignard reagent.

Here's how it proceeds:

1. Reaction with Magnesium in Dry Ether: An alkyl bromide \((R-Br)\) reacts with magnesium \((Mg)\) metal in dry ether (anhydrous diethyl ether) to form a Grignard reagent. The general reaction is:

\[ R-Br + Mg \rightarrow RMgBr \]

This reaction is facilitated by the presence of dry ether, which helps solubilize both the alkyl bromide and the magnesium, allowing them to react. The magnesium inserts itself between the carbon and the bromine, forming an alkylmagnesium bromide \((RMgBr)\) compound.

2. Reaction with Ethanol (EtOH): After the Grignard reagent is formed, it can react with various electrophiles, including aldehydes, ketones, esters, and other compounds with electrophilic carbons. In this case, if the Grignard reagent \((RMgBr)\) is reacted with ethanol \((EtOH)\), the following reaction occurs:

\[ RMgBr + EtOH \rightarrow R-H + MgBrOEt \]

Overall, the sequence of reactions involves the formation of a Grignard reagent by the reaction of an alkyl bromide with magnesium in dry ether, followed by the subsequent reaction of the Grignard reagent with ethanol to produce an alkane.