HR interviews are dreaded for a reason. Very often the questions do not have clear yes or no answers. And the middle ground is what most of us find difficult to tread.
One such question begins with "What if...?"
This is a behavioral event interviewing question which intends to understand the thought process of the candidate in a particular situation.
The first instinct of the candidate is to give his/her verdict on the problem faced in the situation. But that is the catch. The interviewer is actually not interested in the solution to the problem but your problem solving approach.
If you reach your decision on the spur of the moment, it will only reflect poorly on your decision making abilities. And if you keep asking for too many details to aide your decision making, it will still not make you look good because in a real life situation it's never possible to have all the facts available.
The best way to handle the question is to lay out your action plan for problem solving. For example, if the question is "What would you do if your subordinate was underperforming and this has been affecting the team performance adversely."
Now don't get tempted to reply immediately with a decision, sealing the fate of the subordinate.
Pause for a moment then say something like "Fortunately I have been a team leader for last few years and I have faced similar situations in the past. From my experience I've learned that the first crucial step to solving this problem is open communication. Making the other person comfortable so s/he can openly communicate often leads to surprising revelations. It is difficult for employees to admit difficulties like lack of knowledge, unsuccessful time management etc. A private talk in a non-threatening environment helps the employee to come out in the open. Once we agree on what the problem is, we can mutually decide on a solution. When the solution is agreeable to the employee, it becomes easier for him/her to implement it."
Take a few moments to organize your thoughts and come up with a plan of action to resolve the problem. But refrain from taking instantaneous decisions.
HR Interview questions are not something to be scared of. If you think rationally and give logical answers, you have nothing to worry.