Question

Which is the weakest base

• A. NaOH
• B. KOH
• C. Ca(OH)₂
• D. Zn(OH)₂

Answer 1

The correct option is D

Zn(OH)₂

We know that, The normal oxide formed by the elementon extreme left is the most basic (e.g., $N{a}_{2}O$), whereas that formed by the element on extreme right is the most acidic (e.g., $C{l}_2{O}_7$). Oxides of elements in the centre are amphoteric (e.g., $A{l}_2{O}_3,A{s}_2{O}_3$) or neutral (eg., $CO,No,N_{2}O$). Amphoteric oxides behave as acid with bases and as base with acids, whereas neutral oxides have no acidic or basic properties.

With increase in oxidation number acidic character increases and basic character decreases. The oxides formed by element on extreme left is most basic (eg: $N{a}_{2}O$) where as on extreme right is the most acidic (eg. $C{l}_2{O}_7$), oxides of elements in the centre are amphoteric (e.g., $A{l}_2{O}_3,A{s}_2{O}_3$) or neutral (eg. $Co,No,N_{2}O$).

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Therefore, elements from group 1 and 2 are most basic in nature, they do not have acidic character.

While, Zn belongs to the centre part of the periodic table, so it is amphoteric in nature, so it will be basic as well as acidic.

But basic character decreases along the period because electropositivity decreases.

Therefore,

$Zn(OH{)}_2$ will be the weakest base.