I received following questions from a visitor to my website recently: "How should I respond to inappropriate questions such as: (1) Do you have a stable home life? (2) Tell me about your personal situation. Are these inappropriate questions? It has been so long since I interviewed for a job, your suggestions about most helpful responses would be appreciated!" Those are, indeed, inappropriate questions that should NOT be asked at an interview.
Various federal, state, and local laws regulate questions a prospective employer can ask you. An employer's questions — on job application, in interview, or during testing process — must be related to job for which you are applying.
That does not mean, however, that you will never be asked inappropriate questions. Some companies have poor HR support, some interviewers are untrained and unaware of inappropriate or illegal questions, and some even ask them knowing they should not.
You won't have much chance of getting job if you respond to such questions by saying, "Hey, that's an inappropriate question. You can't ask me that!"
So you have a few options. First, you can answer question. Even if it's inappropriate to ask, there's nothing that says you can't answer it. If you choose to do so, realize that you are giving information that is not job-related. You could harm your chances by giving "wrong" answer.
Or you could respond with something like, "How would my answer to that question directly relate to my ability to perform in this position?" If you keep your tone non-confrontational, courteous and upbeat, they may realize they've goofed by asking such a question without getting upset at you for pointing out their mistake. Depending on how they respond, you may feel more comfortable answering.
The best strategy, I believe, is to figure out and address their TRUE CONCERN. When they ask something like, "Do you have a stable personal life?" they may be trying to protect themselves from a bad situation that they've had to deal with in past (former employee whose personal problems interfered with his/her ability to do job). So what they really want to know is, will YOU be a reliable employee who can be counted upon to show up and do your job effectively, regardless of any personal problems you may have.