Easy or Hard?
Questions in the viva do not fall neatly into one of two piles.
Easy and hard are relative terms that don’t help to describe the questions that prompt the kind of discussion found in the viva.
An easy question for one candidate could be very hard for another.
An easy-to-ask question could have a very hard-to-formulate response.
A hard question could have been considered many times before by a candidate, while an easy question has no certain response.
Best to get away from labels of easy and hard completely.
Questions in the viva can be challenging or not. In either case, they are there to drive the discussion. They’re asked with an expectation of a response from the candidate. You can’t predict what questions you will be asked before your viva, but you can prepare yourself to respond to whatever question your examiners bring to you.