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Start with the truth about how the project was chosen, because the interviewer will find it anyway. Many projects come from a list the department gave. Some were the idea of one teammate. Some were picked because a senior had done something similar and the team could get help. None of these is a bad answer. 'Our guide gave us three options and we picked this one because two of us had already worked with the hardware' is honest and specific.
What interviewers hear far too often is the grand reason: a passion for helping farmers, a wish to change healthcare. If that is genuinely why you chose it, say so, and be ready for the next question, which will be about the farmers or the hospital. If it is not, leave it out. A motive that falls apart on the second question does more harm than an ordinary one.
Then move on to the part that matters: what interested you once you started. This is where the real answer lives, because most people do not choose their work for deep reasons, but they do find something in it. Perhaps the data turned out to be messier than you expected and you enjoyed cleaning it. Perhaps you liked talking to the shopkeepers more than writing the code. Perhaps a bug taught you how something worked underneath. One real moment like this tells the interviewer more than any statement about passion.
Keep it short. Thirty seconds to a minute is right. This question usually opens a conversation about the project, and a long answer uses up time you would rather spend on what you built.
If you would choose differently today, it is fine to say so. 'If I started again I would pick something with real users, because testing on our own data hid a lot of problems.' That shows you learned from the project, which is the point of having done one.
Avoid two traps. The first is criticising the department or your guide for the choice. Even if the project was not your preference, the interviewer is listening for how you talk about people you work with. The second is pretending the project is more original than it is. Many final-year projects are versions of common ideas. That is normal. What makes yours worth discussing is what you did with it.
Practise by writing your answer in three sentences: how it was chosen, what interested you, and what you would like to be asked next. Read it aloud to someone who was not on your team. If they ask 'and then what?', you have ended in the right place.