Hard water contains dissolved: MCQ with Answer and Explanation

Hard water contains dissolved:
A. Sodium salts
B. Potassium salts
C. Ammonium salts
D. Calcium and magnesium salts
Answer: Option D
Solution (By JKSSB Mock Tests)
Hardness is caused by Ca²⁺ and Mg²⁺ ions in the form of bicarbonates, sulfates, chlorides. They react with soap to form scum.

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Practice More chemistry Questions

Question #1
Which allotrope of carbon is a good conductor of electricity?
A. Graphite
B. Diamond
C. Buckminsterfullerene
D. Charcoal

Correct Answer: Option A


Explanation:
Graphite conducts electricity due to delocalized electrons within its layers. Diamond is an insulator. Buckminsterfullerene (C₆₀) is a semiconductor but not as good a conductor as graphite in bulk; fullerene solids can be doped to become conductors. Charcoal is a poor conductor. Graphite electrodes are used in batteries and electrolysis.

This question belongs to: Science chemistry
Question #2
Diamond has a high melting point because:
A. It has strong covalent network bonds throughout the crystal
B. It is made of carbon
C. It has weak bonds
D. It has free electrons

Correct Answer: Option A


Explanation:
Diamond is a giant covalent structure where each carbon is tetrahedrally bonded to four others via strong covalent bonds. Melting requires breaking numerous strong bonds, needing very high temperature (~3500°C). Graphite also has high melting point. Molecular solids like ice have low melting points. Carbon alone doesn't guarantee high m.p.; it's the structure.

This question belongs to: Science chemistry
Question #3
The reaction 2H₂O₂ → 2H₂O + O₂ is a:
A. Displacement reaction
B. Decomposition reaction
C. Double displacement reaction
D. Combination reaction

Correct Answer: Option B


Explanation:
Hydrogen peroxide decomposes into water and oxygen. A single reactant breaks down into two or more products, so it is a decomposition reaction. This particular reaction can be catalyzed by MnO₂ or light. It is also a disproportionation redox reaction where O in H₂O₂ (-1) goes to -2 in H₂O and 0 in O₂.

This question belongs to: Science chemistry