Generally you can replac the ending -ity with -idad in Spanish.
ability = habilidad
activity = actividad
authority = autoridad
capacity = capacidad
celebrity = celebridad
charity = caridad
city = ciudad
community = comunidad
electricity = electricidad
identity = identidad
opportunity = oportunidad
personality = personalidad
popularity = popularidad
possibility = posibilidad
priority = prioridad
quality = calidad
quantity = cantidad
reality = realidad
responsibility = responsabilidad
security = seguridad
university = universidad
Some exceptions: majority (mayoría), minority (minoría).
