One Question view(Mobile/Tab) is a feature that allows you to show only one question at a time to the respondents taking the survey on a Mobile or Tablet. Completing the question would take them to the next question. You can enable or disable it from Survey Setting. One question view comes in handy when you have applied logic to the question. In such cases, the next question depends on answer choices and one question view would allow respondents to see only the question that follows the survey path.
This is how it would appear to the respondents if the One Question View(Mobile/Tab) is enabled