Assertion (A): The noble gases are placed in Group 18. Reason (R): They have a completely filled outermost shell (except Helium) and zero valency. MCQ with Answer and Explanation
Assertion (A): The noble gases are placed in Group 18. Reason (R): They have a completely filled outermost shell (except Helium) and zero valency.
A. A is true but R is false.
B. Both A and R are true and R is the correct explanation of A.
C. Both A and R are true but R is NOT the correct explanation of A.
D. A is false but R is true.
Answer: Option B
Solution (By JKExamLibrary)
Noble gases have completely filled valence shells (ns²np⁶, except He which is 1s²), making them highly stable and unreactive with a valency of zero. Because of this unique stability and distinct electronic configuration, they form a separate group, Group 18, in the modern periodic table.
Explanation:
Faraday's first law of electrolysis: Mass of substance deposited or liberated is proportional to the charge passed (m = ZQ). Z is electrochemical equivalent. Second law relates masses of different substances to equivalent weights for same charge. Ohm's law is V=IR, Graham's law for diffusion. Faraday's laws are quantitative.
Explanation:
Magnesium (Z=12): configuration 2,8,2. Period = number of shells = 3; Group = 2 (2 valence electrons). Be is Group 2, Period 2; Ca is Group 2, Period 4; Sr Period 5.
Explanation:
When cement hydrates, it releases heat known as heat of hydration. This exothermic process can cause thermal cracking in massive concrete structures if not controlled. The main compounds C₃S and C₃A have high heat of hydration. For dams, low-heat cement with lower C₃A content is used. Heat of solution is for dissolving, combustion for burning, fusion for melting.
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