You can expect a range of questions from deep dive into your specific milestones and how you plan to reach them and the timetables involved, to who the members of your team are and the chemistry of the team (what happens when things get touch, don't go the way you initially thought, need to tweak or pivot), to your exit strategy and expectations of valuation of the company at exit or perhaps the next milestone (when maybe a VC will come in and buy out the angel).
Investors have to know what's the ROI. So, expect to show how there will be a 10X to 20X return (or more) in the timetable you lay out for the investment. The angel isn't going to get paid based on the revenues of the company, but rather the growth of the valuation of the company (its worth on the market). So, you might even get asked whether the founder(s) are willing to step out of the role of CEO if there's need to bring in someone more experienced and capable to play that role on the team.
You can expect questions about your cap table and how many other investors are involved, how much the founders have invested, how much is common vs preferred stock, what's your strategy against dilution, when is your projected break-even point, what's the protected intellectual property of the company and how is it protected, what's your "secret sauce" and what are your assumptions upon which your 5-year projections are based, and how will you use the funds invested by this particular angel.
These are just a few of the questions I think you will be asked, and should be prepared to address.
The angel is probing to see how well YOU know your business and the market you're entering. So you'll get questions about the competition, your competitive advantage (yes, it's in the biz plan, but be prepared for additional questions), your strategy for market penetration (assuming you already have market validation) and how you expect to overcome setbacks/obstacles/challenges to your assumptions.
The angel will likely ask questions that probe to determine how committed you and your team are to the outcomes, and whether you're prepared to weather any and all storms. Since the road to success is often circuitous, your level of commitment (and flexibility without losing focus on the mission) will probably be the undercurrent of some line of questioning.
And since angels are investing their own money (and not institutional funds), they may have a personal interest in your service or product. They may also be interested in a board seat to have some oversight of their investment.
Be prepared to address the dreaded "burn rate." How much will you spend each month, on what, and why.
Well, that's a lot to think about. I'll leave it there.