Formic acid (methanoic acid) exhibits certain unique and abnormal...

Formic acid ($H-COOH$) possesses a unique structure containing both an aldehydic group and a carboxylic acid group.

Due to the presence of the aldehydic moiety, it acts as a reducing agent. It reduces Tollens' reagent to form a silver mirror and Fehling's solution to form a brick-red precipitate of $Cu_2O$. Thus, statements (1) and (2) are correct.

Heating formic acid with concentrated $H_2SO_4$ leads to its dehydration, producing carbon monoxide ($CO$) gas and water. Thus, statement (4) is correct.

The Hell-Volhard-Zelinsky (HVZ) reaction involves the halogenation of carboxylic acids at the $\alpha$-carbon. This reaction strictly requires the presence of at least one $\alpha$-hydrogen atom. Since formic acid lacks an $\alpha$-carbon atom, it does not contain any $\alpha$-hydrogen atoms and cannot undergo the HVZ reaction. Thus, statement (3) is incorrect.