Question

Assertion : Lithium salts are mostly hydrated.
Reason : The hydration enthalpies of alkali metal ions decrease with increase in ionic sizes.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

Lithium is the smallest in size among the alkali metals. Hence, $Li ^{+}$ion can polarize water molecules more easily than other alkali metals. As a result, water molecules get attached to lithium salts as water of crystallization. Hence, lithium salts such as trihydrated lithium chloride (LiC1.3H20) are commonly hydrated. As the size of the ions increases, their polarizing power decreases. Thus hydration enthalpies decreases. Hence, other alkali metal ions usually form anhydrous salts.