Question

Which one of the following is acid salt?
A. $N{a_2}S$
B. $N{a_2}S{O_3}$
C. $NaHS{O_3}$
D. $N{a_2}S{O_4}$

Answer 1

Hint: We know that salts are the product of neutralization reactions.
In chemistry, acid and bases are quite significant.

Complete step by step answer:
Arrhenius theory: Arrhenius defined acids $\left( {HA} \right)$ and bases $\left( {BOH} \right)$ as ${H^ + }$ and $O{H^ - }$ donors which we can show as follows:
$\begin{array}{c}
HA \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over
{\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} {H^ + } + {A^ - }\\
BOH \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over
{\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} {B^ + } + O{H^ - }
\end{array}$
Brönsted-Lowry theory: As per this theory, acids and bases are donors and acceptors respectively. From here, we also got conjugate acid-base pairs which differ by one ${H^ + }$ . We can see that $HA$ and ${A^ - }$ are conjugate acid-base pair.
Lewis acids–base theory: Here, acids and bases are electron pair acceptors and donors respectively. Before this presence of ${H^ + }$ was a must condition for being an acid but Lewis acids include those also which might not have ${H^ + }$but still act as acids by accepting electrons. For example $B{F_3}$ .
We can classify these acids and bases as weak and strong based on their ability to furnish ${H^ + }$ or $O{H^ - }$. Dissociation constants have been derived from the acid-base equilibria which indicate the strength of the acid or base. Higher the dissociation constant is, stronger is the acid or base.
It has also been established that strong acid has a weak conjugate base and vice versa. Similarly, a strong base has weak conjugate acid and vice versa. So, if it is a strong acid then would be a weak base.
Now, coming to the reactions of acids and bases, we can define the acid-base reactions as neutralization reactions which have salt and water as products. Let’s have a look at the neutralization reaction of $HA$ and $BOH$ :
$HA\left( {acid} \right) + BOH\left( {base} \right) \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over
{\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} BA\left( {salt} \right) + {H_2}O\left( {water} \right)$
We can deduce the nature of the salt based on the nature of acid and base: salt of strong acid and weak base would be acidic and so on.
Now, let’s talk about the given salts and write the chemical equations for their dissociation:
$\begin{array}{c}
N{a_2}S \to 2N{a^ + } + {S^{2 - }}\\
N{a_2}S{O_3} \to 2N{a^ + } + SO_3^{2 - }\\
NaHS{O_3} \to N{a^ + } + HSO_3^ - \\
N{a_2}S{O_4} \to 2N{a^ + } + SO_4^{2 - }
\end{array}$
As we can see that all the given salts are of a strong base$NaOH$ but it is only $NaHS{O_3}$which still contains protons that can be donated further. So, it is an acidic salt.

Therefore, the correct option is option (C).

Note:
It is not only acids and bases that can be acidic or basic but salts can be acidic or basic as well.