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271.
Which of the following statements are correct for alkali metal compounds ?
(i) Superoxides are paramagnetic in nature.
(ii) The basic strengths of hydroxides increases down the group.
(iii) The conductivity of chlorides in their aqueous solutions decreases down the group.
(iv) The basic nature of carbonates in aqueous solutions is due to cationic hydrolysis.

(i), (ii) and (iii) only

(i) and (ii) only

(ii), (iii) and (iv) only

(iii) and (iv) only

(i) and (ii) only

Among the gievn statements, statement (i) and (ii) are correct. Other can be corrected as-

(iii) The conductivity of alkali metal chlorides in their aqueous solution increases on moving down the group because in aqueous solution alkali metal chlorides ionise to give alkali metal ions. On moving down the group the size of alkali metal ion increases, thus degree of hydration decreases, due to this reason their conductivity in aqueous solution increases on moving down the group.

(iv) M₂CO₃ $⇌_{aq . solution}^{Ionisation in} 2 M^{+} + {CO}_{3}^{2 -}$

${CO}_{3}^{2 -}$ + 2H₂O → H₂CO₃ + 2OH^-

272.

CaOCl₂ + H₂O → Ca(OH)₂ + X

X + CH₃CHO → Y

Y + Ca(OH)₂ → CHCl₃

What is 'Y'?

CH₃CH(OH)₂
CH₂Cl₂
CCl₃CHO
CCl₃COCH₃

273.

Among the following, which is water insoluble?

Sodium fluoride
Potassium fluoride
Beryllium fluoride
Magnesium fluoride

274.

Solvay process is used in the manufacture of

K₂CO₃
KHCO₃
Na₂CO₃
CaCl₂

275.

Assertion (A) - K, Rb and Cs form superoxides.

Reason (R) - The stability of the superoxides increases from K to Cs due to decrease in lattice energy.

The correct answer is

Both (A) and (R) are true and (R) is the correct explanation of (A).
Both (A) and (R) are true but (R) is not the correct explanation of (A).
(A) is true but (R) is not true.
(A) is not true but (R) is true.

276.

In photoelectric effect, if the energy required to overcome the attractive forces on the electron, (work functions) of Li, Na and Rb are 2.41 eV, 2.30 eV and 2.09 eV respectively, the work function of 'K could approximately be in eV.