Step 1: Identify the reagent.
\(H_2CN_2\) represents diazomethane (\(CH_2N_2\)).
Diazomethane is a methylating agent.
Step 2: Role of \(HBF_4\).
Strong acid protonates diazomethane to generate \(CH_3^+\)-like species.
This methyl group then reacts with alcohol oxygen.
Step 3: Product formed.
Alcohol is converted into methyl ether:
\[
ROH \rightarrow ROCH_3
\]
Final Answer:
\[
\boxed{ROCH_3}
\]