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JEE Main 2020 · Chemistry · s-Block, p-Block Elements and Hydrogen · easy

Group 2 elements and their compounds is correct?

Single correct option

Which of the following statements about group 2 elements and their compounds is correct?
  1. A. Be(OH)2\mathrm{Be(OH)_2} dissolves in both acids and excess NaOH, whereas Mg(OH)2\mathrm{Mg(OH)_2} dissolves only in acids.
  2. B. Solubility of the sulphates increases down the group because hydration enthalpy falls more slowly than lattice enthalpy.
  3. C. Thermal stability of the carbonates decreases from BeCO3\mathrm{BeCO_3} to BaCO3\mathrm{BaCO_3}.
  4. D. Beryllium imparts a characteristic crimson colour to the flame like strontium.
Show answer and solution

Answer: (A) Be(OH)2\mathrm{Be(OH)_2} dissolves in both acids and excess NaOH, whereas Mg(OH)2\mathrm{Mg(OH)_2} dissolves only in acids.

Be(OH)2\mathrm{Be(OH)_2} is amphoteric (forms [Be(OH)4]2−\mathrm{[Be(OH)_4]^{2-}} with excess alkali) while Mg(OH)2\mathrm{Mg(OH)_2} is basic: statement 1 is true. Sulphate solubility decreases down the group because hydration enthalpy decreases faster than lattice enthalpy; carbonate stability increases down the group (smaller polarisation of CO32−\mathrm{CO_3^{2-}} by bigger cations); Be, being small with a high ionisation energy, gives no flame colour.
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