CODE:MN9
📘 Welcome
Hi User, you have selected Read Mode.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
Q1. What type of reaction occurs when calcium oxide and water combine to form a single product, calcium hydroxide?
A combination reaction is one in which two or more substances combine to form a single product. Here, calcium oxide (CaO) and water (H₂O) combine to form calcium hydroxide [Ca(OH)₂], which is a single product. Decomposition is the opposite (one substance breaks down). Displacement involves one element replacing another. Double displacement involves exchange of ions between two compounds. So combination reaction is correct.
Q2. Quick lime
Quick lime is the common name for calcium oxide (CaO). It is obtained by heating limestone (calcium carbonate) strongly. Calcium carbonate is limestone, calcium hydroxide is slaked lime, and calcium chloride is a different compound. So calcium oxide is correct.
Q3. Quick lime is calcium oxide, with the chemical formula CaO.
The chemical formula of quick lime (calcium oxide) is CaO. It has one calcium atom and one oxygen atom. Ca(OH)₂ is calcium hydroxide (slaked lime), CaCO₃ is calcium carbonate (limestone/marble), and H₂O is water. So CaO is correct.
Q4. In the reaction CaO(s) + H₂O(l) → Ca(OH)₂(aq), what is observed regarding temperature?
The reaction between quick lime (CaO) and water is highly exothermic — it releases a large amount of heat. The temperature of the mixture increases significantly, sometimes even causing the water to boil. Temperature does not decrease (that would be endothermic), and it does not become cold. So a large amount of heat is released is correct.
Q5. What is the product formed when calcium hydroxide reacts with carbon dioxide in the air during whitewashing?
When calcium hydroxide [Ca(OH)₂] (slaked lime) is applied to walls, it reacts slowly with carbon dioxide (CO₂) in the air to form calcium carbonate (CaCO₃) and water. The reaction is: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. Calcium carbonate gives a shiny finish to the walls. Calcium oxide is quick lime, calcium chloride would require chlorine, and calcium sulphate would require sulphur. So calcium carbonate is correct.
Q6. What gives a shiny finish to walls after whitewashing?
When a whitewash solution (calcium hydroxide in water) is applied to walls, it reacts with carbon dioxide in the air to form calcium carbonate (CaCO₃). This calcium carbonate forms a hard, shiny, and protective layer on the walls over time. Calcium hydroxide itself is the whitewash solution, not the shiny finish. Calcium oxide is quick lime. So calcium carbonate gives the shiny finish.
Q7. What is the chemical formula of marble?
Marble is a form of calcium carbonate (CaCO₃). It is a metamorphic rock made of calcite. Limestone, chalk, and marble all have the same chemical formula — CaCO₃. CaO is quick lime, Ca(OH)₂ is slaked lime, and CO₂ is carbon dioxide. So CaCO₃ is correct.
Q8. Which of the following is a combination reaction?
In option C, carbon (C) and oxygen (O₂) combine to form a single product — carbon dioxide (CO₂). This is a combination reaction. Option A is decomposition (one substance breaks into two). Option B is displacement (Zn replaces Cu). Option D is neutralisation (acid + base → salt + water), which is a double displacement reaction. So C + O₂ → CO₂ is correct.
Q9. In simple language, what defines a combination reaction?
A combination reaction is defined as a reaction in which two or more reactants combine to form a single product. For example, A + B → AB. A single substance breaking down is decomposition. Two compounds exchanging ions is double displacement. Heat absorption is endothermic, not a defining feature of combination. So two or more substances combine to form a single product is correct.
Q10. What is the product in the combination reaction: 2H₂(g) + O₂(g) → ?
Hydrogen gas (H₂) reacts with oxygen gas (O₂) to form water (H₂O). The balanced equation is 2H₂ + O₂ → 2H₂O. Water is the product. H₂O₂ is hydrogen peroxide, which is formed in a different reaction. HO₂ is not a stable compound. H₂O is the formula, but since the equation has 2H₂, the product must be 2H₂O to balance. So 2H₂O is correct.
Q11. Reactions in which heat is released along with the formation of products are called what?
Exothermic reactions are reactions that release heat energy to the surroundings. The word “exo” means outward. Endothermic reactions absorb heat. Thermal reactions simply involve heat but do not specify release or absorption. Combination reactions may be exothermic or endothermic, but not all combination reactions release heat. So exothermic reactions is correct.
Q12. The reaction between quicklime and water to form slaked lime is an example of what kind of reaction?
The reaction CaO + H₂O → Ca(OH)₂ is a combination reaction because two substances combine to form one product. It is also exothermic because it releases a large amount of heat. It is not endothermic (heat is released, not absorbed) and not decomposition (one substance is not breaking down). So exothermic and combination is correct.
Q13. Which of the following is an exothermic reaction?
Burning of natural gas (methane) is a combustion reaction that releases a large amount of heat and light — so it is exothermic. Evaporation of water absorbs heat (endothermic), melting of ice absorbs heat (endothermic), and photosynthesis absorbs sunlight energy (endothermic). So burning of natural gas is exothermic.
Q14. What process in our body is described as an exothermic process?
Respiration is an exothermic process. In respiration, glucose reacts with oxygen in our cells to release energy, carbon dioxide, and water. This energy is used to keep us alive. Digestion is the breakdown of food (some parts release energy, but respiration is the specific energy-releasing process). Thinking and breathing in are not energy-releasing chemical reactions. So respiration is correct.
Q15. During respiration, what does glucose combine with in our cells to provide energy?
During respiration, glucose (C₆H₁₂O₆) combines with oxygen (O₂) in the cells to produce carbon dioxide, water, and energy. The equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy. Nitrogen is not involved, carbon dioxide is a product, and water is a product. So oxygen is correct.
Q16. What are rice, potatoes, and bread broken down into during digestion?
Rice, potatoes, and bread are rich in carbohydrates (starches). During digestion, these complex carbohydrates are broken down into simpler sugars, mainly glucose. Glucose is the form that cells can use for respiration to produce energy. Proteins break down into amino acids, and fats break down into fatty acids and glycerol. So glucose is correct.
Q17. What is the special name for the reaction where glucose provides energy by combining with oxygen?
The reaction where glucose combines with oxygen to release energy is called respiration. It occurs in the cells of living organisms. Combustion is the burning of a substance in oxygen (usually with a flame) — it is similar but occurs outside the body. Digestion is the breakdown of food into simpler substances. Photosynthesis is the process by which plants make glucose. So respiration is correct.
Q18. Which of the following is also an example of an exothermic reaction?
Decomposition of vegetable matter into compost is an exothermic process — it releases heat over time (the compost pile feels warm). Formation of ice releases heat (freezing is exothermic), but it is a physical change, not a chemical reaction. Dissolving salt in water is generally a slight endothermic or neutral process (some salts release heat, but NaCl is neutral). Boiling water is endothermic (absorbs heat). So decomposition into compost is the best example of an exothermic chemical reaction.
Q19. In the balancing steps for Fe + H₂O → Fe₃O₄ + H₂, what was done first to balance oxygen atoms?
In the skeletal equation Fe + H₂O → Fe₃O₄ + H₂, oxygen is unbalanced. Fe₃O₄ has 4 oxygen atoms, so to balance oxygen, we put a coefficient of 4 in front of H₂O: Fe + 4H₂O → Fe₃O₄ + H₂. This gives 4 oxygen atoms on the left and 4 on the right. We do not change the formula H₂O (that would be wrong). So put coefficient 4 as 4 H₂O is correct.
Q20. When balancing an equation, what must we remember NOT to alter?
When balancing a chemical equation, we must NOT change the chemical formulae (the subscripts inside the formula). Changing the formula would change the substance itself. We can change coefficients (numbers in front of formulae), we can change the order of substances (though not necessary), and we can add physical states. So the formulae of the compounds or elements is correct.
Q21. In the partly balanced equation Fe + 4H₂O → Fe₃O₄ + H₂, which element was balanced next?
After balancing oxygen by putting 4H₂O, the equation is: Fe + 4H₂O → Fe₃O₄ + H₂. Now oxygen is balanced (4 on each side). Iron is unbalanced (1 on left, 3 on right). Hydrogen is unbalanced (8 on left, 2 on right). The next step is to balance hydrogen by putting a coefficient of 4 in front of H₂: Fe + 4H₂O → Fe₃O₄ + 4H₂. So hydrogen was balanced next.
Q22. To equalise hydrogen atoms in the partly balanced equation, what coefficient was placed before H₂?
In Fe + 4H₂O → Fe₃O₄ + H₂, the left side has 4H₂O, which gives 8 hydrogen atoms. The right side has H₂, which gives 2 hydrogen atoms. To balance hydrogen, we put a coefficient of 4 in front of H₂: Fe + 4H₂O → Fe₃O₄ + 4H₂. Now the right side has 8 hydrogen atoms. So the coefficient is 4.
Q23. After balancing hydrogen, which element was left to be balanced in the equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂?
After balancing hydrogen (with 4H₂ and 4H₂O), the equation is: Fe + 4H₂O → Fe₃O₄ + 4H₂. Oxygen is balanced (4 on left, 4 on right). Hydrogen is balanced (8 on left, 8 on right). Iron is unbalanced — left side has 1 Fe, right side has 3 Fe (in Fe₃O₄). So iron is left to be balanced. Water is a reactant, not an element to balance.
Q24. What coefficient was placed before Fe to balance the iron atoms?
To balance iron atoms, we put a coefficient of 3 in front of Fe: 3Fe + 4H₂O → Fe₃O₄ + 4H₂. Now left side has 3 Fe atoms, and right side has 3 Fe atoms (in Fe₃O₄). So the coefficient before Fe is 3.
Q25. What is the final balanced equation for the reaction between iron and steam?
The balanced equation for the reaction of iron with steam is: 3Fe + 4H₂O → Fe₃O₄ + 4H₂. Check: Left — Fe=3, H=8, O=4. Right — Fe=3 (in Fe₃O₄), H=8 (in 4H₂), O=4 (in Fe₃O₄). All are balanced. Option C is the correct balanced equation.
Q26. What is the method of balancing chemical equations described in the text called?
The method described in the text for balancing chemical equations is the hit-and-trial method. In this method, we adjust coefficients by trial and error (with the help of atom counting) until the equation is balanced. The algebraic method uses variables, the oxidation number method is for redox reactions, and inspection method is another name but the text specifically uses “hit-and-trial”. So hit-and-trial method is correct.
Q27. In the hit-and-trial method, what do we use to balance the equation?
In the hit-and-trial method, we adjust coefficients (numbers placed before formulae) to balance the equation. The coefficients should be the smallest possible whole numbers (integers). We do not change subscripts (that would change the formula). We do not use fractions (though sometimes used temporarily and then multiplied to get whole numbers). We do not ignore elements. So use the smallest whole number coefficients is correct.
Q28. What is the correct order of steps taken to balance Fe + H₂O → Fe₃O₄ + H₂?
The steps in balancing Fe + H₂O → Fe₃O₄ + H₂ were: Step 1 — Balance oxygen (put 4H₂O). Step 2 — Balance hydrogen (put 4H₂). Step 3 — Balance iron (put 3Fe). So the correct order is oxygen, then hydrogen, then iron. So balance O, then H, then Fe is correct.
Q29. After putting the coefficient 4 for H₂O, how many oxygen atoms are on the left side?
After putting 4H₂O, the left side has 4 water molecules. Each H₂O has 1 oxygen atom. So 4 × 1 = 4 oxygen atoms on the left side. Fe₃O₄ has 4 oxygen atoms on the right side, so oxygen is balanced. So 4 is correct.
Q30. After putting the coefficient 4 for H₂, how many hydrogen atoms are on the right side?
After putting 4H₂, the right side has 4 hydrogen molecules. Each H₂ has 2 hydrogen atoms. So 4 × 2 = 8 hydrogen atoms on the right side. The left side has 4H₂O, which also has 8 hydrogen atoms (4 × 2 = 8). So hydrogen is balanced. So 8 is correct.
Q31. In the final check of the balanced equation, what must be equal on both sides?
In checking a balanced chemical equation, we must verify that the number of atoms of each element is the same on both sides. This ensures mass conservation. The number of molecules may differ. Total mass being equal is the consequence of equal atoms, but the direct check is on atoms. Physical states are not required for balance. So number of atoms of each element is correct.
Q32. In the respiration equation, what are the products?
The respiration equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy. The products are carbon dioxide (6CO₂), water (6H₂O), and energy (released as heat). Glucose and oxygen are reactants, not products. So carbon dioxide, water, and energy is correct.
Q33. What is the primary purpose of respiration at the cellular level?
The primary purpose of respiration at the cellular level is to provide energy. Glucose is broken down in the presence of oxygen to release energy that is used for all life processes (growth, movement, thinking, etc.). Absorbing oxygen and releasing carbon dioxide are steps in the process, but the ultimate goal is energy production. So to provide energy is correct.
Q34. What type of reaction is the burning of coal (C + O₂ → CO₂)?
The burning of coal is: C + O₂ → CO₂. Two substances (carbon and oxygen) combine to form a single product (carbon dioxide), so it is a combination reaction. It also releases a large amount of heat and light, so it is exothermic. It is not decomposition (one substance breaking down) or displacement. So exothermic combination is correct.
Q35. In the reaction for burning natural gas, what is the coefficient of O₂?
The balanced equation for burning natural gas (methane) is: CH₄ + 2O₂ → CO₂ + 2H₂O. The coefficient of O₂ is 2. This gives 4 oxygen atoms on the left (2 × 2 = 4) and 4 on the right (2 in CO₂ + 2 in 2H₂O). So the coefficient of O₂ is 2.
Q36. Which activity in the chapter involves a combination reaction that gives out heat?
Activity 5.1 involves burning of magnesium ribbon (2Mg + O₂ → 2MgO) — a combination reaction that releases heat and light (exothermic). Activity 5.4 involves the reaction of calcium oxide with water (CaO + H₂O → Ca(OH)₂) — also a combination reaction that releases heat (exothermic). Both are exothermic combination reactions. So both Activity 5.1 and 5.4 is correct.
Q37. What is the physical state of water (H₂O) in the respiration equation?
In the respiration equation, water is produced in the liquid state — (l). Respiration in cells produces water as a liquid (though it may be present in cellular fluids). It is not gas (steam), not aqueous (dissolved in water would be redundant since it is water), and not solid (ice). So (l) is correct.
Q38. In the partly balanced equation (Step IV), Fe + 4H₂O → Fe₃O₄ + 4H₂, which element is still unbalanced?
In Fe + 4H₂O → Fe₃O₄ + 4H₂, oxygen is balanced (4 on left, 4 on right). Hydrogen is balanced (8 on left, 8 on right). Iron is unbalanced — left side has 1 Fe, right side has 3 Fe (in Fe₃O₄). So iron is still unbalanced.
Q39. What is the total number of hydrogen atoms on the left in the final balanced equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂?
In the final balanced equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂, the left side has 4H₂O. Each H₂O has 2 hydrogen atoms. So 4 × 2 = 8 hydrogen atoms on the left side. The right side has 4H₂, which also has 8 hydrogen atoms (4 × 2 = 8). So total hydrogen atoms on the left is 8.
Q40. What is the key characteristic used to identify a reaction as a combination reaction?
The key characteristic of a combination reaction is that two or more substances (reactants) combine to form a single product. For example: A + B → AB. Release of heat (exothermic) is not always true for combination reactions (some are endothermic). Formation of precipitate and evolution of gas are not defining features. So formation of a single product from multiple reactants is correct.
Q41. What solution is used for whitewashing walls?
The solution used for whitewashing walls is a suspension of calcium hydroxide [Ca(OH)₂] in water, commonly called lime water or whitewash. It is prepared by adding water to quick lime (CaO) to form slaked lime [Ca(OH)₂]. Calcium oxide in water would be the same as making slaked lime, but the whitewash solution itself contains calcium hydroxide. So calcium hydroxide in water is correct.
Q42. Why is the reaction between calcium oxide and water considered exothermic?
The reaction CaO + H₂O → Ca(OH)₂ is exothermic because it releases a large amount of heat. The beaker becomes hot, and sometimes the water boils. It does not absorb heat (that would be endothermic), there is a temperature change (it increases), and it does not make the beaker cold (it becomes hot). So it releases a large amount of heat is correct.
Q43. According to the text, what provides us with the energy to stay alive?
The food we eat provides us with energy to stay alive. Food contains carbohydrates (like glucose), fats, and proteins that are broken down during digestion and respiration to release energy. Water is essential for life but does not provide energy. Air (oxygen) is needed for respiration but does not directly provide energy (it is used to oxidise food). Sleep helps restore the body but does not provide energy directly. So the food we eat is correct.
Q44. In the context of balancing, what does the term “smallest whole number coefficient” refer to?
In balancing chemical equations, we use the smallest possible whole number coefficients. This means using integers (1, 2, 3, 4, etc.) and not fractions (like ½, ¾) or decimals. Subscripts are part of formulae and are not changed. Coefficients of 1 are used but not always (sometimes larger numbers are needed). So using coefficients like 1, 2, 3, etc., not fractions is correct.
Q45. What is the correct way to write “four water molecules” when balancing an equation?
The correct way to write four water molecules is 4H₂O (or 4 H₂O with a space). The coefficient 4 is placed in front of the formula H₂O. H₂O₄ would mean a different compound (4 oxygen atoms in one molecule, which is not water). (H₂O)₄ is not standard notation. H₄O₂ would be a different compound. So 4 H₂O is correct.
Q46. After balancing, the final equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂ has how many iron atoms on each side?
In the final balanced equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂, the left side has a coefficient of 3 before Fe, so 3 iron atoms. The right side has Fe₃O₄, which has 3 iron atoms (subscript 3). So iron atoms are 3 on both sides. So 3 on left, 3 on right is correct.
Q47. Which of these everyday processes is NOT mentioned as exothermic in the text?
The text mentions burning of natural gas, respiration, and decomposition of vegetable matter into compost as exothermic processes. Photosynthesis is NOT mentioned as exothermic — in fact, it is an endothermic process because it absorbs sunlight energy to convert CO₂ and H₂O into glucose and oxygen. So photosynthesis is correct.
Q48. What happens to the reaction mixture in an exothermic reaction?
In an exothermic reaction, heat is released to the surroundings. This causes the reaction mixture to warm up (its temperature increases). It does not cool down (that would be endothermic). Colour change and gas evolution are not always observed in exothermic reactions. So it warms up is correct.
Q49. In the balancing process, what was the state of the equation after Step V?
After Step V, the equation was fully balanced. The steps were: Step I — skeletal equation, Step II — count atoms, Step III — balance oxygen (4H₂O), Step IV — balance hydrogen (4H₂), Step V — balance iron (3Fe), Step VI — check. After Step V, the equation 3Fe + 4H₂O → Fe₃O₄ + 4H₂ was fully balanced. So fully balanced is correct.
Q50. What is the main reason for balancing a chemical equation using the hit-and-trial method?
The main reason for balancing a chemical equation (using any method, including hit-and-trial) is to obey the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction. Balancing ensures that the number of atoms of each element is the same on both sides. It is not for neatness, adding physical states, or identifying reaction type (though balance helps in understanding). So to obey the law of conservation of mass is correct.