$Zn{(OH)_2}$ is a:
A. Acidic base
B. Diacidic base
C. Triacidic base
D. Tetracidic base

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Hint: Zinc hydroxide is basically an amphoteric oxide , that is it is not actually an acid or a base individually but behaves as both an acid and base. Thus,it will dissolve readily in a dilute solution of a strong acid,such as HCl, and also in a solution of an alkali such as NaOH.

Complete answer: equivalent concept can be mathematically written as:
Equivalent weight= $n \times mole$
Where n is n-factor. Since n-factor is different and can change in any reaction. Equivalent weight is a variable quantity. However, molar weight is a fixed quantity. n-factor depends upon various factors such as acidity and basicity. In the above question we are asked about acidity of zinc hydroxide. Therefore let us understand what acidity depends upon:
Acidity for bases can be defined as the number of replaceable hydroxide ions in the compound or number of moles of ${(OH)^ - }$ ions given by 1 mole of base. Also it can be defined as number of moles of ${H^ + }$ taken by base.
We know that metal oxides, carbonates or bi-cabonates form basic hydroxides. Therefore the zinc hydroxide above is a basic hydroxide as it is made from the metal zinc.
In an aqueous solution zinc hydroxide displaces into $Z{n^{2 + }}and \,2{(OH)^ - }$ . Therefore we observe that there are two replaceable hydroxide ions and which makes it a diacidic base.

Hence the correct option is B.

Note:The other factors that the n-factor depends upon are: normality, valency and basicity. Zinc hydroxide is an inorganic chemical compound and occurs naturally. It reacts with both acids and bases.