Questionnaires form part of a survey – used to collect qualitative and/or quantitative data.
Ethical questions are not leading (see earlier example of “What is your religion?”).
Can ask open-ended questions to avoid bias – “What do you think of the website?” – encourages feelings or ideas to be expressed.
However, open-ended questions can be time-consuming, responses are hard to control and responses are difficult to synthesis and group into categories for analysis.