Salesforce Admin was trying to do an upload through data loader. His update is for an account picklist field that has restricted values. What will happen to his upload when he adds a new picklist field that doesn’t exist among the restricted values?

Answer options:

A.The value will be added to the picklist field
B.The value will be added as an inactive picklist value
C.The record will fail, and the value will be blocked
D.The record will be updated without any issues

Correct Answer: C 
If the picklist fields have the restrict picklist to the values defined in the value set enabled, then it won`t allow values other than the defined. 
Other options are incorrect because the picklist value fields are restricted so any new value cannot be added and the record cannot be updated. 
Reference:

https://developer.salesforce.com/forums/?id=9060G000000UZP2QAO