All three statements are correct. Formic acid (HCOOH) dimerizes via strong intermolecular hydrogen bonds, increasing its effective molecular weight and boiling point. Water (H₂O), ammonia (NH₃), and hydrogen fluoride (HF) exhibit anomalously high boiling points within their respective groups (VIA, VA, VIIA) due to extensive hydrogen bonding. Methane (CH₄) has the lowest boiling point among CH₄, SiH₄, GeH₄, and SnH₄ because London dispersion forces, the only intermolecular forces present, increase with molecular size and mass; CH₄ is the smallest and lightest.

These forces generally increase with increasing molecular weight and size. Moving down the group from PH₃ to BiH₃, the size and mass of the central atom increase (P < As < Sb < Bi), leading to stronger van der Waals forces and an increase in boiling points in the order PH₃ < AsH₃ < SbH₃ < BiH₃.

Final Answer: All are correct