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One Chapter, Five Types, Almost Guaranteed Marks
A chemical reaction is any change in which the substances you start with are rearranged into new substances with new properties. A chemical equation is simply that change written in symbols, with reactants on the left and products on the right.
A physical change — ice melting, sugar dissolving — is reversible and creates nothing new. A chemical change — milk turning sour, iron rusting — makes a new substance and is usually hard to reverse. That single distinction alone appears in almost every general science paper.
Why this chapter pays: the questions are classification questions, not calculations. If you can name the five reaction types and recognise one example of each, you can answer an item you have never seen. SSC, Railway, CTET and BPSC TRE-4 Part II all draw from the same small pool of examples.
1. A chemical equation has to be balanced in order to satisfy which law?
2. In the reaction 2Mg + O₂ → 2MgO, magnesium is:
3. Which of the following is a double displacement reaction?
4. Silver chloride turns grey when kept in sunlight: 2AgCl → 2Ag + Cl₂. This is an example of:
5. Which gas is evolved when zinc granules are added to dilute sulphuric acid?
6. Packets of chips are filled with which gas to prevent rancidity?
7. Galvanisation protects iron from rusting by coating it with a layer of:
8. Respiration in living cells is best described as which kind of reaction?