Which salt causes permanent hardness? MCQ with Answer and Explanation

Which salt causes permanent hardness?
A. Mg(HCO₃)₂
B. CaSO₄
C. Na₂CO₃
D. Ca(HCO₃)₂
Answer: Option B
Solution (By JKSSB Mock Tests)
Calcium sulfate and magnesium sulfate/chloride cause permanent hardness. Bicarbonates cause temporary hardness removable by boiling.

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Practice More chemistry Questions

Question #1
If the half-life of a radioactive substance is 10 days, what fraction of the original substance will remain after 30 days?
A. 1/2
B. 1/16
C. 1/4
D. 1/8

Correct Answer: Option D


Explanation:
The number of half-lives elapsed is 30 days / 10 days = 3. The fraction remaining is (1/2)ⁿ, where n is the number of half-lives. So, (1/2)³ = 1/8. After 10 days: 1/2; after 20 days: 1/4; after 30 days: 1/8 of the original amount remains.

This question belongs to: Science chemistry
Question #2
Which method is used for the concentration of an ore based on the difference in density between the ore and impurities?
A. Leaching
B. Hydraulic washing
C. Magnetic separation
D. Froth flotation

Correct Answer: Option B


Explanation:
Hydraulic washing (or gravity separation) is based on the difference in specific gravities (densities) of the ore and the gangue (impurities). The powdered ore is washed with a stream of water; lighter impurities are washed away, leaving the heavier ore particles behind.

This question belongs to: Science chemistry
Question #3
The maximum number of electrons that can be associated with the quantum numbers n=3, l=1, m=-1 is:
A. 2
B. 6
C. 1
D. 10

Correct Answer: Option A


Explanation:
The quantum numbers n=3 and l=1 specify the 3p subshell. The magnetic quantum number m=-1 specifies one particular 3p orbital within that subshell. According to Pauli's Exclusion Principle, a single orbital can accommodate a maximum of two electrons, which must have opposite spins (+1/2 and -1/2).

This question belongs to: Science chemistry