"the chill outside" and "by the kitchen instead" will be the most appropriate one to determine the meaning of alfresco.
Step-by-step explanation:
Alfresco means eating or eaten in the open air.
Option 1: the host greeted us: This does not speak about the process of eating or air. Hence, invalid.
Option 2: the crowded cafe: This does not mean alfresco.
Option 3: briefly debated: Debate means arguing. So this stands invalid
Option 4: "Chill outside": The text means open air. So this is valid
Option 5: "by the kitchen instead": This text stands right because, it talks something related to cooking / eating.