Temporary hardness of water is caused by: MCQ with Answer and Explanation

Question
Temporary hardness of water is caused by:
A. Calcium sulfate
B. Calcium chloride
C. Sodium chloride
D. Magnesium bicarbonate
Answer: Option D
Solution (By JKSSB Mock Tests)
Temporary hardness is due to dissolved bicarbonates of Ca and Mg. These can be removed by boiling, which precipitates carbonates. Calcium sulfate and chloride cause permanent hardness. Sodium chloride does not cause hardness. Boiling: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. Bicarbonates are formed when water containing CO₂ passes over limestone.
This question belongs to: Science chemistry
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Question #1
John Dalton is known for:
A. Atomic theory
B. Periodic table
C. Discovery of electron
D. Neutron
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Correct Answer: Option A

Explanation:
John Dalton put forward the atomic theory in 1808, proposing that matter is made of indivisible atoms, atoms of same element are identical, and compounds are combinations of atoms. Electron was discovered by J.J. Thomson, periodic table by Mendeleev, neutron by Chadwick.
This question belongs to: Science chemistry
Question #2
During electrolysis, reduction occurs at the:
A. Cathode
B. Electrolyte
C. Salt bridge
D. Anode
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Correct Answer: Option A

Explanation:
Cathode is where reduction (gain of electrons) takes place in both electrolytic and galvanic cells. Anode is where oxidation occurs. Mnemonic: RED CAT (Reduction at Cathode), AN OX (Oxidation at Anode).
This question belongs to: Science chemistry
Question #3
In the electrolysis of acidified water, the gas collected at the cathode is:
A. Oxygen
B. Nitrogen
C. Hydrogen
D. Chlorine
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Correct Answer: Option C

Explanation:
During the electrolysis of water, reduction occurs at the cathode (negative electrode), where H⁺ ions gain electrons to form hydrogen gas (2H⁺ + 2e⁻ → H₂). Oxidation occurs at the anode, producing oxygen gas. The volume of H₂ collected is exactly twice that of O₂.
This question belongs to: Science chemistry
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