An organic compound [A] has molecular formula . When compound [A] is treated with , it yields…

An organic compound [A] has molecular formula $\text{C}_7\text{H}_6\text{O}_2$. When compound [A] is treated with $\text{SOCl}_2$, it yields compound [B]. On heating with $\text{NH}_3$, compound [B] forms compound [C]. Compound [C] forms compound [D] on reaction with $\text{Br}_2/\text{KOH}$. Compound [D] responds to carbylamine test. Identify compounds [A], [B], [C] and [D].