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Subjects

Science

Chemical Reactions and Equations

रासायनिक अभिक्रियाएँ और समीकरण

In Class 10 Science, under the chapter Chemical Substances – Nature and Behaviour, this topic introduces chemical reactions as changes that form new substances. Students learn to identify reactants and products, represent reactions through word and chemical equations, and write balanced equations using correct chemical formulae while following the law of conservation of mass.

Practice questions

Why is a precipitate shown by a downward arrow in a chemical equation?When copper oxide is heated with hydrogen, the black substance becomes reddish brown. What does this prove?Why is hydrogen oxidised in the reaction between copper oxide and hydrogen?A student claims that in the reaction 2Mg + O₂ → 2MgO, magnesium is reduced because it combines with oxygen. What is the correct evaluation of this claim?Why are oxidation and reduction understood together in a redox reaction?Which pair is most essential for rusting of iron?Why can rusting start when the paint layer on iron is scratched?What is the main reason why an oiled iron object rusts less?What is the basic chemical cause of rancidity of oils and fats?What is the most correct reason why oily food kept in warm open air spoils quickly?How does a nitrogen filled packet protect oily food?How is the reaction Zn + CuSO₄ → ZnSO₄ + Cu most accurately classified?If a container becomes cold and gas also evolves what is the most careful conclusion?If heat is written on the product side and the container is hot what is the correct conclusion?When an iron nail is placed in a blue copper sulphate solution, the solution gradually turns green and a reddish-brown coating forms on the nail. What type of reaction is this?Why is respiration considered different from combustion yet an energy releasing chemical process?What is the correct difference in direction of energy between photosynthesis and respiration?In an unknown process a new substance formed gas evolved and total mass remained same in a closed container. What is the most suitable conclusion?In a closed container, gas and a precipitate both form during a reaction, but nothing escapes. What is the correct conclusion about mass?Why can a lower measured mass after gas escapes from an open container give a wrong conclusion?