-Questionnaires can be seen in three categories. The first is the closed ended or structured ones, the second is open ended or unstructured ones, and the last is a mixture of closed ended and openended questionnaires. 

-Actually it can be said that closed ended questionnaires give the researcher
quantitative or numerical data and open-ended ones give qualitative or text information.

-To exemplify, when a participant of study is distant, the researcher may send the questionnaire by post. But the return rate of them become quite low.
Moreover, they can be delivered online. In this process, the rate of return may be slightly higher as it is easier for respondents to reply.