This e-book serves as a revision and practice guide, primarily focusing on questions and answers. It contains over 250 questions, featuring exam-style inquiries along with detailed explanations and helpful hints to enhance recall and understanding. The book includes various types of questions, such as theoretical, numerical, fill-in-the-blank, and multiple-choice questions. Calculators may be used for both numerical and multiple-choice questions. The questions are designed for a Bachelor of Science (B.Sc.) level audience. Topics covered (i) Orbital Angular Momentum and Quantization, (ii) Quantum Theory of the Hydrogen Atom (including hydrogen-like atoms), and (iii) the Stern-Gerlach Experiment and Electron Spin.