The element with atomic number 20 has the electronic configuration: MCQ with Answer and Explanation

Question
The element with atomic number 20 has the electronic configuration:
A. 2,8,8,2
B. 2,8,10
C. 2,8,8,4
D. 2,8,18,2
Answer: Option A
Solution (By JKSSB Mock Tests)
Atomic number 20 is calcium (Ca). Electron shells fill according to 2n²: K=2, L=8, M can hold 18 but fourth shell (N) starts after 8 electrons in M due to energy level considerations (Aufbau principle). So Ca configuration is 2,8,8,2. It has 2 valence electrons, belongs to Group 2, Period 4. Its nearest noble gas is Ar (2,8,8).
This question belongs to: Science chemistry
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Question #1
Identify the correct statement regarding the physical properties of matter.
A. Liquids have a definite volume but no definite shape.
B. Gases have the highest density among the three states.
C. Solids have the maximum intermolecular space.
D. Gases cannot be compressed.
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Correct Answer: Option A

Explanation:
Liquids have a definite volume but take the shape of their container. Solids have the least intermolecular space and highest density. Gases have maximum intermolecular space and are highly compressible. This relates directly to the kinetic theory of matter, which describes particle arrangement and movement in different states.
This question belongs to: Science chemistry
Question #2
The hardness of water that cannot be removed by boiling is called:
A. Softness
B. Alkalinity
C. Permanent hardness
D. Temporary hardness
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Correct Answer: Option C

Explanation:
Permanent hardness is due to dissolved sulfates and chlorides of calcium and magnesium. Boiling does not remove it. It requires chemical treatment (washing soda, ion exchange) or distillation. Temporary hardness (bicarbonates) is removed by boiling.
This question belongs to: Science chemistry
Question #3
Graham's law relates rates of diffusion to:
A. Pressure
B. Molar mass
C. Volume
D. Temperature
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Correct Answer: Option B

Explanation:
Rate ∝ 1/√(molar mass) at constant T and P. Lighter gases diffuse faster. This is Graham's law of diffusion/effusion.
This question belongs to: Science chemistry
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