According to Avogadro's law, equal volumes of different gases at the same temperature and pressure contain the same number of:

1. The law is about counting particles rather than weighing them. 2. According to Avogadro's law, equal volumes of gaseous nitrogen, hydrogen and ammonia contain the same number of molecules. 3. That holds at the same temperature and pressure. 4. Since the molecules differ in mass, the samples would not weigh the same. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 9 'Gases', sections 9.1-9.6_