NCERT MCQ Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations

Evaporation is a physical process where water changes from liquid to gas due to temperature, without any chemical change in composition. No new substance is formed, so it is not a chemical reaction.

In this reaction, two elements—magnesium and oxygen—combine to form a single product, magnesium oxide. This is characteristic of a combination reaction where two or more reactants form one compound.

On heating, calcium carbonate (CaCO₃) breaks down into calcium oxide (CaO) and carbon dioxide (CO₂). This breakdown of a single compound into simpler substances classifies it as a decomposition reaction.

Silver reacts slowly with hydrogen sulfide in the air, forming a black compound called silver sulfide. This process is corrosion, a gradual deterioration of metal due to chemical reactions.

Combustion is an exothermic reaction that releases heat and light energy. Methane burns in oxygen to form carbon dioxide and water, releasing significant energy to the surroundings.

Iron is more reactive than copper and displaces copper from copper sulfate solution, forming iron sulfate and depositing copper metal. This is a classic displacement reaction.

Magnesium burns with intense white light in air, producing magnesium oxide as a white powder. This reaction is highly exothermic and visually striking due to the bright flame.

Redox reactions involve simultaneous oxidation (loss of electrons) and reduction (gain of electrons). One substance is oxidized and another is reduced, making both processes occur together.

In this reaction, the ions of two compounds exchange places to form a precipitate (BaSO₄) and a salt (NaCl), which characterizes a double displacement reaction.

Rancidity occurs when fats and oils react with oxygen, producing unpleasant smells and tastes. It is a form of slow oxidation that degrades food quality over time.

Heating ferrous sulfate causes it to decompose into ferric oxide (Fe₂O₃), a brown solid and releases sulfur dioxide and sulfur trioxide gases, evident from the smell and fumes.

Calcium hydroxide reacts with carbon dioxide in the air to form calcium carbonate, a white precipitate. This is used as a test for carbon dioxide presence in air.

Electrolysis of water produces hydrogen and oxygen gases. Hydrogen is produced in double the volume because each water molecule contains two hydrogen atoms and one oxygen atom.

Iron displaces copper from copper sulfate solution, causing reddish-brown copper to deposit on the nail, changing its appearance. This is a displacement reaction based on reactivity.

When solutions of barium chloride and sodium sulfate mix, they form barium sulfate, an insoluble white precipitate. This is a hallmark of double displacement reactions.

Respiration breaks down glucose to release energy in the form of ATP. It is an exothermic reaction because energy is released during the oxidation of glucose.

Corrosion is a slow chemical process where metals react with air, moisture or chemicals, causing deterioration. Examples include rusting of iron and tarnishing of silver.

Silver chloride undergoes photodecomposition in sunlight, forming grey-colored silver and chlorine gas. It is a common example of a photochemical reaction.

Zinc displaces hydrogen from sulfuric acid to form zinc sulfate and hydrogen gas. This is a single displacement reaction driven by zinc’s higher reactivity.

Antioxidants inhibit oxidation reactions in food, extending shelf life and preventing spoilage. They help protect food from turning rancid due to oxygen exposure.