Talk to your recruiter if you are uncertain about whether a specific question is acceptable. Set the place and time of the interview, and confirm the logistics with the candidate. Find a quiet place to conduct the interview, free from distractions and interruptions. Block uninterrupted time for the interview. Do not take calls or allow other distractions.
Interruptions give applicants the impression that they are a low priority.
Interviews typically last from 30 to 90 minutes depending on the amount of information you need, and interruptions can needlessly extend the length of the interview.