A free original English–Hindi lesson on matter, mixtures and separation for RRB Group D science foundations. Distinguish physical state from element, compound and mixture; use particle models and combined observations to compare solutions, suspensions and colloids. Choose a separation from the relevant property difference, the component to recover and the method’s limits. Worked cases, labelled representations, an analogy, a quick reference and five questions with full explanations support these decisions. The concentration-by-mass example is optional and excluded from compulsory review. These are descriptions for reasoning, not chemical-handling instructions; clear or separated water is not automatically safe to drink. This is a focused topic resource, not complete chemistry or General Science coverage.