Temporary hardness of water can be removed by: MCQ with Answer and Explanation

Question
Temporary hardness of water can be removed by:
A. Adding sodium chloride
B. Boiling
C. Filtration
D. Adding calcium sulfate
Answer: Option B
Solution (By JKSSB Mock Tests)
Boiling converts soluble bicarbonates of Ca and Mg to insoluble carbonates: Ca(HCO₃)₂ (heat) → CaCO₃↓ + H₂O + CO₂, which can then be filtered. Permanent hardness (due to sulfates/chlorides) is not removed by boiling; requires washing soda, ion exchange, or calgon. Calcium sulfate addition would increase permanent hardness. Filtration removes solid particles, not dissolved ions.
This question belongs to: Science chemistry
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Question #1
A gas at 300 K occupies 2 L. If the temperature is raised to 600 K at constant pressure, the volume becomes:
A. 2 L
B. 1 L
C. 6 L
D. 4 L
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Correct Answer: Option D

Explanation:
Charles' law: V₁/T₁ = V₂/T₂. V₂ = V₁ × T₂/T₁ = 2 L × 600 K / 300 K = 4 L. Volume doubles as absolute temperature doubles. Note: must use Kelvin, not Celsius. (600 K = 327°C). If mass and pressure are constant, volume is directly proportional to absolute temperature.
This question belongs to: Science chemistry
Question #2
The maximum number of electrons that can be accommodated in the N shell is:
A. 18
B. 50
C. 32
D. 8
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Correct Answer: Option C

Explanation:
The maximum number of electrons in a shell is given by the formula 2n², where n is the principal quantum number. For the N shell, n = 4. Thus, maximum electrons = 2(4)² = 2(16) = 32. The K, L, M, and N shells hold 2, 8, 18, and 32 electrons respectively.
This question belongs to: Science chemistry
Question #3
Which of the following is an electrolyte?
A. Ethanol
B. Sugar solution
C. Distilled water
D. Aqueous solution of NaCl
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Correct Answer: Option D

Explanation:
An electrolyte is a substance that produces ions when dissolved in water or melted, allowing the solution to conduct electricity. Aqueous NaCl dissociates into Na⁺ and Cl⁻ ions. Distilled water, sugar, and ethanol do not form ions in solution and are therefore non-electrolytes.
This question belongs to: Science chemistry
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