35 multiple-choice questions in College Board exam style. Each has four choices and a full explanation of why each option is right or wrong.
Always measure angles from the normal, not the surface. This is the single most common source of careless mistakes in this unit.
Remember which direction light bends. Entering a higher-index medium bends toward the normal; entering a lower-index medium bends away from the normal.
For mirror/lens questions, sketch a quick ray diagram even if you're solving algebraically. It catches sign errors before they become wrong final answers.
Read the explanations even when you got it right. Each one teaches a small fact that often returns in a different form on the exam.