Question

Thermal stability order of Group 1 hydroxides is:

• A. LiOH $<$ NaOH $<$ KOH $<$ RbOH $<$ CsOH
• B. CsOH $<$ RbOH $<$ KOH $<$ NaOH $<$ LiOH
• C. LiOH $>$ NaOH $>$ KOH $>$ RbOH $>$ CsOH
• D. LiOH = NaOH = KOH = CsOH

Hint:

In Group 1, thermal stability of hydroxides increases down the group due to decreasing cationic charge density and polarization.

Answer 1

The Correct Option is A

Thermal Stability of Group 1 Hydroxides

Group 1 hydroxides are of the form \( \text{M}OH \), where \( \text{M} \) is an alkali metal.

Concept: 

The thermal stability of hydroxides increases down the group.

This is because as the size of the cation increases (from Li⁺ to Cs⁺), the polarizing power decreases. Lower polarizing power means less distortion of the OH⁻ ion, leading to greater thermal stability.

Therefore, the order is:

\( \text{LiOH} < \text{NaOH} < \text{KOH} < \text{RbOH} < \text{CsOH} \)

Correct Option: Option 1