Question

Which of the following is a strong base?
A. Acetic acid
B. Hydrochloric acid
C. Sodium bicarbonate
D. Sodium hydroxide

Answer 1

According to Arrhenius theory, acid is a substance that gives ${H^ + }$ ions on dissolving in the aqueous solution. It increases the concentration of ${H^ + }$ ions in the solution. The base is a substance that gives $O{H^ - }$ ion on dissolving in the aqueous solution. The concentration of $O{H^ - }$ ions is high in the solution.

Complete answer: Strong bases are characterized by the fact that they dissociate completely in aqueous solution. In the given above options sodium hydroxide $NaOH$ , is said to be a strong base because it dissociates completely in aqueous solution to form sodium cations, $N{a^ + }$ and hydroxide anions, $O{H^ - }$ .
So, we have
$NaO{H_{\left( {aq} \right)}} \to Na_{(aq)}^ + + OH_{\left( {aq} \right)}^ -$
Since one formula unit of sodium hydroxide contains 1 sodium ion and 1 hydroxide ion, it follows that one mole will contain one mole of sodium cations and one mole of hydroxide anions.
So we can say that every mole of sodium hydroxide dissolved in solution will produce one mole of hydroxide anions, which have a direct impact on the pH of the solution.
The hydroxide ion makes sodium hydroxide a strong base that reacts with acids to form water and the corresponding salts.
For example – sodium hydroxide with hydrochloric acid forms sodium chloride and water.
$NaO{H_{\left( {aq} \right)}} + HC{l_{\left( {aq} \right)}} \to NaC{l_{\left( {aq} \right)}} + {H_2}{O_{\left( l \right)}}$
Hence option (D) sodium hydroxide is the right answer.

Note:
Arrhenius theory is also known as “electrolytic dissociation”.
Water is a neutral substance, which does not conduct electricity. By dissolving some substance in water, it conducts electricity. These substances are called electrolytes and the process is known as “electrolytic dissociation”.