Assertion (A): Aluminum is highly reactive but is used for making cooking utensils. Reason (R): Aluminum forms a protective layer of aluminum oxide on its surface. MCQ with Answer and Explanation
Assertion (A): Aluminum is highly reactive but is used for making cooking utensils. Reason (R): Aluminum forms a protective layer of aluminum oxide on its surface.
A. A is false but R is true.
B. Both A and R are true and R is the correct explanation of A.
C. Both A and R are true but R is NOT the correct explanation of A.
D. A is true but R is false.
Answer: Option B
Solution (By JKSSB Mock Tests)
Aluminum is a highly reactive metal, yet it is widely used for cookware. This is because it rapidly reacts with atmospheric oxygen to form a thin, tough, and invisible layer of aluminum oxide (Al2O3) on its surface. This passivation layer prevents further corrosion and reaction with food.
Explanation:
Soap (sodium carboxylate) reacts with Ca²⁺/Mg²⁺ to form insoluble calcium or magnesium carboxylate (scum). This precipitates and reduces cleaning efficiency. Sodium and potassium salts are soluble. This is why detergents, which form soluble Ca/Mg salts, are used. Scum is visible in hard water areas.
Explanation:
Endothermic reactions absorb heat from the surroundings. The decomposition of calcium carbonate (CaCO₃ → CaO + CO₂) requires continuous heating to proceed. Burning of gas, respiration, and the reaction of sodium with water are all exothermic reactions that release significant amounts of heat energy to the surroundings.
Assertion (A): Leguminous plants do not require nitrogenous fertilizers. Reason (R): They have Rhizobium bacteria in their root nodules that fix atmospheric nitrogen.
A.A is false but R is true.
B.Both A and R are true but R is NOT the correct explanation of A.
C.A is true but R is false.
D.Both A and R are true and R is the correct explanation of A.
Explanation:
Leguminous plants (like peas, beans) have a symbiotic relationship with Rhizobium bacteria in their root nodules. These bacteria convert atmospheric N₂ into usable nitrogen compounds, fulfilling the plant's nitrogen needs. Thus, they generally do not need external nitrogenous fertilizers. Both statements are correct and R explains A.
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