Which of the following is considered an illegal interview question?

The question about having children is considered illegal because it can lead to potential discrimination based on family status or gender. In many jurisdictions, asking about family life, including whether someone has children or plans to have them, is seen as infringing on privacy and potentially leading to biases against candidates, particularly women. This question does not pertain directly to the individual's qualifications or abilities related to the job, and therefore it is not appropriate to ask in an interview setting.

Conversely, the other questions directly relate to the candidate's skills, work ethic, and professional aspirations, making them legitimate inquiries during the hiring process. These types of questions help employers assess how well a candidate may fit the role without crossing legal boundaries.