Which of the following is formed as a by product of decomposition of arenediazonium fluoroborate to give fluorobenzene?

BF₃

The correct answer is option 4. \(BF_3\).

When arenediazonium fluoroborate (\(\text{C}_6\text{H}_5\text{N}_2\text{BF}_4\)) decomposes, the reaction proceeds as follows:

Formation of Fluorobenzene: One of the products formed is fluorobenzene (\(\text{C}_6\text{H}_5\text{F}\)).

Release of Nitrogen Gas \((N_2)\): Nitrogen gas \((N_2)\) is liberated as a by-product.

Formation of Boron Trifluoride \((BF_3)\): The three remaining fluorine atoms from the arenediazonium fluoroborate combine with boron from \(\text{BF}_4^-\) to form boron trifluoride (\(\text{BF}_3\)).

Therefore, the overall reaction can be summarized as:

This decomposition process results in the formation of fluorobenzene, nitrogen gas, and boron trifluoride as products.