Hi!
For a question such as this one, it's usually most effective to choose one or two key motivations and then support them with a strong and detailed example that clearly demonstrates your drive.
The aim is to show depth rather than listing lots of motivations without evidence. If you feel you have multiple motivations, you can mention them briefly, but it's best to focus the example around one main motivation and show tangible actions or results - what you did, why you did it and what the outcome was. A concise STAR-style structure could work well to help demonstrate where you demonstrated your drive and motivation.
For example:
- State what motivates you (e.g. problem-solving, responsibility, working under pressure, learning new skills, making an impact, etc.)
- Give a strong example that illustrates your motivation in action (structuring it using a STAR-style structure)
- Link it back to why that makes you suited to the role of a trainee solicitor / Arnold & Porter
Quality over quantity tends to leave a stronger impression - I would try to prioritise reflection and depth over listing multiple examples. I hope that helps, and best of luck with your application!