Atoms, Elements, Compounds & Mixtures - Science MCQs for PST JEST EST Jobs 2026
Atoms, Elements, Compounds & Mixtures MCQs - PST JEST EST Learn atoms, elements, compounds and mixtures with easy theory and 10 solved MCQs for PST, JEST and EST jobs test preparation in Sindh. PST/JEST/EST, MCQs, Online Test, Jobs 2026 Atoms, Elements, Compounds & Mixtures Science Notes and MCQs for PST, JEST and EST Jobs Theory and Key Notes Atom: the smallest unit of an element. It has a nucleus (protons + neutrons) and electrons moving around it. Proton has positive charge, electron has negative charge, neutron has no charge. Atomic number = number of protons. Mass number = protons + neutrons. Element: pure substance made of one kind of atom only (e.g. Hydrogen, Oxygen, Iron). Compound: two or more elements chemically combined in a fixed ratio (e.g. water H2O, salt NaCl). Mixture: two or more substances physically mixed, no fixed ratio (e.g. air, sea water, milk). Symbols from Latin names: Sodium = Na, Potassium = K, Iron = Fe, Gold = Au, Silver = Ag...