Stability of hydrides decreases down a group (weaker E-H bond): NH3 > PH3 > AsH3 > SbH3 > BiH3. Reducing character increases down the group (less stable = more reactive): BiH3 > SbH3 > AsH3 > PH3 > NH3. Acid strength of binary hydrides increases across a period (electronegativity) and down a group (bond strength): HF < HCl < HBr < HI (down group). NH3 < H2O < HF (across period). Boiling points: Anomalously high for NH3, H2O, HF due to hydrogen bonding. PH3 < NH3 (H-bonding raises NH3 b.p.); H2S < H2O (H-bonding raises H2O b.p.). Among HX: HF has highest b.p. (H-bonding), then HI > HBr > HCl (van der Waals forces dominate for Cl-I).