You are planning to set up an Azure Free Account. Would the credit in the Azure Free Account expire after a specific period of time?

Answer options:

A.Yes
B.No

Answer – A 
After a duration of 30 days or if the 200 USD credit gets over, then you have to convert your Free subscription to a Pay-As-You-Go subscription. 
This is also mentioned in the FAQ section for the Azure Free Account. 

For more information on the commonly asked questions for the Azure Free account, please visit the below URL- 

https://azure.microsoft.com/en-us/free/free-account-faq/