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NaOH is a strong base because:
(A) it gives OH ion
(B) it can be oxidised
(C) it ionises completely
(D) both A and C

Answer
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Hint: Sodium hydroxide or caustic soda or NaOH is a base. It is strong alkali having pH value 12 and for concentrated solutions, the value is 13–14. Sodium metal belongs to alkali metal, so its hydroxide is basic. Strength means the extent of dissociation. Check the products of its dissociation.

Complete step by step answer:
One formula unit of sodium hydroxide or NaOH contains one sodium cation and one hydroxide anion. Or, we can say that its one mole contains one mole of sodium cations and one mole of hydroxide anions. On dissociation it, gives NaOHNa++OH.
NaOH is basic. Let us discuss that. There are three different concepts of acid and bases. One, Arrhenius, other is Bronsted-Lowry and Lewis theory. Let us discuss
S. No. Name of theoryDefinition of these theories and reason for its acidity and basicity
1.ARRHENIUS CONCEPTBases are species that contains hydroxyl (OH) ions or produce OH ions on ionization. NaOH on its dissociation produces OH ions . So, it is a base.
2.BRONSTED-LOWRY CONCEPTBases are species that have the ability to accept hydrogen ions (H+) . NaOH reacts with strong acid HCl to produce salt NaCl and water. This is an example of a neutralisation reaction. So,NaOHionises to form OH ions which in turn will accept the H+ ions coming from HCl, forming out water (H2O).


The correct answer to this question is option (D), both A and C.

Additional information:
Application of sodium hydroxide:
(1) Sodium hydroxide is extensively used in the paper industry.
(2) It is used in the Bayer process of aluminium production.

Note: The answer to this question can be interpreted practically. Caustic soda solution is basic, so can be identified through the litmus test. Red litmus will convert to a blue colour when it comes in contact with the base solution. So, NaOH is a base.