Ammonia gas does not burn itself nor is it helpful in burning other substances. It does not burn when ammonia gas is ignited in the air. But it starts burning due to excess of oxygen. She extinguishes when a burning candle is carried in a jar of ammonia gas.
The critical temperature of ammonia is 133°C. Therefore, it keeps on increasing pressure at normal temperature.
The boiling point of liquid ammonia is -33.4°C and freezing point -77.7°C. Ammonia has a higher boiling point than phosphine(PH3). The reason for this is that the negative efficiency of nitrogen is higher than the negative efficiency of phosphorus. Hence intermolecular hydrogen bonding occurs in ammonia. And more energy is required to separate its molecules.