Choose the correct statement from the following :
(1) The standard enthalpy of formation for alkali metal bromides becomes less negative on descending the group.
(2) The low solubility of CsI in water is due to its high lattice enthalpy.
(3) Among the alkali metal halides, LiF is least soluble in water.
(4) LiF has least negative standard enthalpy of formation among alkali metal fluorides.
Correct answer: (3) Among the alkali metal halides, LiF is least soluble in water.
Explanation:
1. Standard enthalpy of formation for alkali metal bromides becomes more negative on descending down the group.
2. In case of CsI, lattice energy is less, but Cs+ is having less hydration enthalpy due to which it is less soluble in water.
3. For alkali metal fluorides, the solubility in water increases from lithium to caesium. LiF is least soluble in water.
4. Standard enthalpy of formation for LiF is most negative among alkali metal fluorides.