1. Picric acid has three –NO₂ groups which are strong electron-withdrawing groups.
2. These groups stabilize the conjugate base (picrate ion) by resonance and –I effect.
3. Formic acid has only one –COOH group, so its conjugate base is less stabilized.
4. Greater stabilization of conjugate base ⇒ higher acidity, so picric acid is stronger.

HCOOH (Picric Acid)

Picric acid is soluble in NaHCO₃ solution?

Picric acid (2,4,6-trinitrophenol) is a strong acid due to the presence of three –NO₂ groups, which strongly withdraw electrons and stabilize the phenoxide ion. Because of this high acidity, it can react even with a weak base like NaHCO₃.

Reaction:
Picric acid + NaHCO₃ → Sodium picrate (soluble) + CO₂ + H₂O

So, it dissolves in NaHCO₃ with effervescence of CO₂ gas.