ANSWER: [A] Explanation: Correct option: (a) The near point of his eyes has receded away. The student can clearly see the blackboard but cannot read his textbook, which means he suffers from hypermetropia (farsightedness). In this defect, the near point of the eye shifts farther away than normal, maRead more
ANSWER: [A]
Explanation: Correct option: (a) The near point of his eyes has receded away. The student can clearly see the blackboard but cannot read his textbook, which means he suffers from hypermetropia (farsightedness). In this defect, the near point of the eye shifts farther away than normal, making nearby objects appear blurred.
ANSWER: [C] Explanation: Correct option: (c) 40 cm. To obtain an image of magnification M = − 1, the image must be real, inverted and of the same size as the object. This happens when the object is placed at twice the focal length of a convex lens. The given focal length is f = 20 cm. Hence, the objRead more
ANSWER: [C]
Explanation: Correct option: (c) 40 cm. To obtain an image of magnification M = − 1, the image must be real, inverted and of the same size as the object. This happens when the object is placed at twice the focal length of a convex lens. The given focal length is f = 20 cm. Hence, the object should be placed at 2f = 40 cm. At this position, the image is formed on the opposite side of the lens, also at 40 cm, with the same size as the object but inverted.
(i) Aluminium forms a thin protective oxide layer (Al₂O₃) on its surface when exposed to air. This layer prevents further corrosion, unlike iron which forms rust (Fe₂O₃·xH₂O) that flakes off. (ii) The dull appearance can be prevented by polishing or anodizing the aluminium surface to maintain its shRead more
(i) Aluminium forms a thin protective oxide layer (Al₂O₃) on its surface when exposed to air. This layer prevents further corrosion, unlike iron which forms rust (Fe₂O₃·xH₂O) that flakes off.
(ii) The dull appearance can be prevented by polishing or anodizing the aluminium surface to maintain its shine and protect it from corrosion.
(iii) Aluminium is lightweight, corrosion-resistant, and durable, making it ideal for roofing, whereas iron sheets are heavier and prone to rusting, requiring more maintenance.
(i) Name element ‘Z’. Element ‘Z’ is Potassium (K) (or any alkali metal like Sodium, Na, depending on context). It is highly reactive, especially with oxygen. (ii) Explain the method used to extract ‘Z’ from its ore. Since Potassium is very reactive, it cannot be reduced by carbon. It is extracted uRead more
(i) Name element ‘Z’. Element ‘Z’ is Potassium (K) (or any alkali metal like Sodium, Na, depending on context). It is highly reactive, especially with oxygen.
(ii) Explain the method used to extract ‘Z’ from its ore. Since Potassium is very reactive, it cannot be reduced by carbon. It is extracted using electrolysis of its molten compound, usually potassium chloride (KCl).
(iii) Write the chemical equation involved in the extraction. Electrolysis of molten potassium chloride:
ANSWER: [D] Explanation: A is false but R is true. Step 1 – Carbon’s behavior: Carbon has 4 valence electrons. To achieve noble gas configuration, it does not strongly lose or gain electrons because gaining 4 electrons or losing 4 electrons is difficult. Instead, it shares electrons to form covalentRead more
ANSWER: [D]
Explanation: A is false but R is true.
Step 1 – Carbon’s behavior:
Carbon has 4 valence electrons. To achieve noble gas configuration, it does not strongly lose or gain electrons because gaining 4 electrons or losing 4 electrons is difficult. Instead, it shares electrons to form covalent bonds.
Step 2 – Reason (R):
R is correct: Carbon has 4 valence electrons and tends to share electrons, forming covalent bonds with itself or other elements.
Step 3 – Relation:
A is false (because carbon prefers sharing, not losing/gaining electrons).
R is true (carbon shares electrons).
A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his text book. Which of the following statements is correct?
ANSWER: [A] Explanation: Correct option: (a) The near point of his eyes has receded away. The student can clearly see the blackboard but cannot read his textbook, which means he suffers from hypermetropia (farsightedness). In this defect, the near point of the eye shifts farther away than normal, maRead more
ANSWER: [A]
Explanation: Correct option: (a) The near point of his eyes has receded away. The student can clearly see the blackboard but cannot read his textbook, which means he suffers from hypermetropia (farsightedness). In this defect, the near point of the eye shifts farther away than normal, making nearby objects appear blurred.
See lessTo get an image of magnification – 1 on a screen using a lens of focal length 20 cm, the object distance must be:
ANSWER: [C] Explanation: Correct option: (c) 40 cm. To obtain an image of magnification M = − 1, the image must be real, inverted and of the same size as the object. This happens when the object is placed at twice the focal length of a convex lens. The given focal length is f = 20 cm. Hence, the objRead more
ANSWER: [C]
Explanation: Correct option: (c) 40 cm. To obtain an image of magnification M = − 1, the image must be real, inverted and of the same size as the object. This happens when the object is placed at twice the focal length of a convex lens. The given focal length is f = 20 cm. Hence, the object should be placed at 2f = 40 cm. At this position, the image is formed on the opposite side of the lens, also at 40 cm, with the same size as the object but inverted.
See lessThe aluminium sheets used in building roofs do not rust, but their surfaces turn dull over time. (i) Why does aluminium not rust like iron? (ii) How can the dull appearance of aluminium be prevented? (iii) Why is aluminium preferred for roofing over iron sheets?
(i) Aluminium forms a thin protective oxide layer (Al₂O₃) on its surface when exposed to air. This layer prevents further corrosion, unlike iron which forms rust (Fe₂O₃·xH₂O) that flakes off. (ii) The dull appearance can be prevented by polishing or anodizing the aluminium surface to maintain its shRead more
(i) Aluminium forms a thin protective oxide layer (Al₂O₃) on its surface when exposed to air. This layer prevents further corrosion, unlike iron which forms rust (Fe₂O₃·xH₂O) that flakes off.
(ii) The dull appearance can be prevented by polishing or anodizing the aluminium surface to maintain its shine and protect it from corrosion.
(iii) Aluminium is lightweight, corrosion-resistant, and durable, making it ideal for roofing, whereas iron sheets are heavier and prone to rusting, requiring more maintenance.
See lessAn element ‘Z’ is highly reactive, reacts with oxygen to give a white solid, and cannot be obtained by reduction with carbon. (i) Name element ‘Z’. (ii) Explain the method used to extract ‘Z’ from its ore. (iii) Write the chemical equation involved in the extraction.
(i) Name element ‘Z’. Element ‘Z’ is Potassium (K) (or any alkali metal like Sodium, Na, depending on context). It is highly reactive, especially with oxygen. (ii) Explain the method used to extract ‘Z’ from its ore. Since Potassium is very reactive, it cannot be reduced by carbon. It is extracted uRead more
(i) Name element ‘Z’. Element ‘Z’ is Potassium (K) (or any alkali metal like Sodium, Na, depending on context). It is highly reactive, especially with oxygen.
(ii) Explain the method used to extract ‘Z’ from its ore. Since Potassium is very reactive, it cannot be reduced by carbon. It is extracted using electrolysis of its molten compound, usually potassium chloride (KCl).
(iii) Write the chemical equation involved in the extraction. Electrolysis of molten potassium chloride:
See lessAssertion (A): Carbon has a strong tendency to either loss or gain electrons to attain noble gas configuration. Reason (R): Carbon has 4 electrons in its outermost shell and has the tendency to share electrons with carbon or other elements.
ANSWER: [D] Explanation: A is false but R is true. Step 1 – Carbon’s behavior: Carbon has 4 valence electrons. To achieve noble gas configuration, it does not strongly lose or gain electrons because gaining 4 electrons or losing 4 electrons is difficult. Instead, it shares electrons to form covalentRead more
ANSWER: [D]
Explanation: A is false but R is true.
Step 1 – Carbon’s behavior:
Carbon has 4 valence electrons. To achieve noble gas configuration, it does not strongly lose or gain electrons because gaining 4 electrons or losing 4 electrons is difficult. Instead, it shares electrons to form covalent bonds.
Step 2 – Reason (R):
R is correct: Carbon has 4 valence electrons and tends to share electrons, forming covalent bonds with itself or other elements.
Step 3 – Relation:
See lessA is false (because carbon prefers sharing, not losing/gaining electrons).
R is true (carbon shares electrons).