In this question, we are asked to identify a kingdom among the given countries.
Option 1: Egypt is not a kingdom. It is a republic, with a president as its head of state.
Option 2: Lebanon is also not a kingdom. It is a parliamentary democratic republic, with a president as its head of state.
Option 3: Thailand is the correct answer. It is a kingdom, officially known as the Kingdom of Thailand. It is a constitutional monarchy, with a king as its head of state. The current king of Thailand is King Maha Vajiralongkorn.
Option 4: Vietnam is not a kingdom. It is a socialist republic, with a president as its head of state.
In summary, among the given options, the only country that is a kingdom is Thailand.