Assertion and Reason Questions for Class 11 Chemistry Chapter 10 The s-Block Elements

Directions:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Q.1. Assertion : BeSO₄ is soluble in water while BaSO₄ is not.
Reason : Hydration energy decreases down the group from Be to Ba and lattice energy remains almost constant.

Answer

Answer:(a)

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Q.2. Assertion : The ionization enthalpies of alkali metals increase progressively as we move down the group form Li to Cs.

Reason : The ionic radii increase as we move down the group from Li to Cs.

Answer

Answer:(d) : The ionization enthalpies of alkali metals decrease progressively as we move down the group from Li to Cs.

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Q.3. Assertion : Lithium salts are hydrated.
Reason : Lithium has higher polarising power than other alkali metal group members.

Answer

Answer:(c) : Li+ has maximum degree of hydration due to its small size and for this reason lithium salts are mostly hydrated.

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Q.4. Assertion : s-block elements are highly electropositive.
Reason : The valence electrons present in s-orbital are loosely held.

Answer

Answer:(a) : The loosely held s-electron in the outermost valence shell of these elements makes them the most electropositive metals which readily give ions, M+ or M2+.

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Q.5. Assertion : The carbonate of lithium decomposes easily on heating to form lithium oxide and CO₂.
Reason : Lithium being very small in size polarises large carbonate ion leading to the formation of more stable Li₂O and CO₂.

Answer

Answer:(a)

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Q.6. Assertion : Generally alkali and alkaline earth metals form superoxides.
Reason : There is a single bond between O and O in superoxides.

Answer

Answer:(c) : Only K, Rb and Cs from alkali metals form superoxides and superoxides possess three electron bond

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Q.7. Assertion : The solubility of the alkaline earth metal hydroxides in water increases with increase in atomic number down the group.

Reason : The alkaline earth metal hydroxides are basic in character. The only exception is Be(OH)₂ which is amphoteric.

Answer

Answer:(b) : The solubility of the alkaline earth metal hydroxides in H2O increases with increase in atomic number down the group. This is due to the reason that both lattice energy and hydration energy decrease down the group as the size of the cation increases but lattice energy decreases more rapidly than the hydration energy and hence, their solubility increases down the group.

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Q.8. Assertion : Electrode potential is a measure of the tendency of an element to lose electrons in the aqueous solution. So, the reducing property can be correlated in terms of electrode potentials (E°) of alkali metals.

Reason : More negative is the electrode potential, higher is the tendency of the element to loose electrons and hence, stronger is the reducing agent.

Answer

Answer:(a)

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Q.9. Assertion : Beryllium carbonate is kept in the atmosphere of carbon dioxide.
Reason : Beryllium carbonate is unstable and decomposes to give beryllium oxide and carbon dioxide.

Answer

Answer:(a)

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Q.10. Assertion : The first element (Li) of group I differs considerably from the rest of the elements of the same group.

Reason : Lithium has small ionic and atomic radii, high electronegativity and ionization enthalpy, high polarising power of its cation and absence of d-electrons in its valence shell compared to rest of the elements of the same group.

Answer

Answer:(a)

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