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, represented as \( \text{M}OH \), consist of an alkali metal \( \text{M} \).

Concept:

The thermal stability of these hydroxides enhances progressively down the group.

This is attributed to the increasing size of the cation from Li⁺ to Cs⁺, which leads to a reduction in polarizing power. A diminished polarizing power results in less distortion of the OH⁻ ion, thereby increasing thermal stability.

Consequently, the stability order is established as:

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

Correct Option: Option 1