Explanation:

- Riot: This is a public disturbance created by a group of people who assemble with a common purpose, often resulting in violence. It's an offence against public tranquility.

- Affray: This involves fighting in a public place, causing terror to the people present. It's also an offence that disturbs public peace.

- Unlawful assembly: This involves a group of people gathering with the intent to commit a crime or to disturb public peace. It is considered an offence against public tranquility.

- Assault: This involves an individual threatening or attempting to harm another person. It is a personal crime, rather than one against public tranquility.

Assault is not an offence against public tranquility.