s-Block Elements — JEE Main · 2021 · 26 Aug 2021 · Shift 2 Question with Solution

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Barium carbonate is insoluble in water and is highly stable.
Reason (R): The thermal stability of the carbonates increases with increasing cationic size. Choose the most appropriate answer from the options given below:

(A)(A) is false but (R) is true.
(B)(A) is true but (R) is false.
(C)Both (A) and (R) are true but (R) is not the true explanation of (A).
(D)Both (A) and (R) are true and (R) is the true explanation of (A).✓ Correct

Answer: (D)

Solution

Barium carbonate is only sparingly soluble in water and decomposes to the oxide only at a very high temperature, so the assertion is true. Down group 2 the cation grows larger and its polarising power falls, so it distorts the carbonate ion less and weakens the

C - O

bonds less; more heat is then needed to pull

C O_{2}

away, and thermal stability rises with cationic size, which makes the reason true. Since

B a^{2 +}

is the largest of the common alkaline earth cations, this trend is exactly what accounts for the high stability of

BaC O_{3}

. Both the assertion and the reason are true, and the reason is the true explanation of the assertion.

JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Single correct option

JEE Main · 2021 · 26 Aug 2021 · Shift 2 · s-Block Elements

Solution

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