Consider the following statements. 

1. Baking soda is an acidic salt whereas washing soda is a basic salt. 
2. The aqueous solution of common salt does not change the colour of either red litmus solution or blue litmus solution. 
3. Amla tastes sour whereas soap solution is bitter in taste. 
4. The water extract of spinach does not change the colour of the blue litmus solution. 

Which of the statements are correct?

When an acid and a base combine, a salt is often the result of the reaction. For instance, sodium chloride, a salt, is created when sodium hydroxide and water combine to make hydrochloric acid. There are three types of salts: basic, neutral, and acid salts. A neutral salt is created when a strong base and strong acid react. A basic salt is decreased when a strong base and weak acid react. An acidic salt is created when a strong acid combines with a weak base.

While washing soda is a basic salt, baking soda is an acidic salt. On the other hand, the following equation demonstrates that the aqueous solution of common salt is neutral by nature:

$\mathrm{NaCl}\left(s\right)+{\mathrm{H}}_2\mathrm{O}\left(l\right)\to {\mathrm{Na}}^{+}\left(aq\right)+{\mathrm{Cl}}^{-}\left(aq\right)$

Thus, neither the colour of the red litmus solution nor the colour of the blue litmus solution is altered by the aqueous solution of common salt.
Additionally, soap has a bitter flavour because it includes caustic soda or sodium hydroxide, whereas amla contains ascorbic acid and tastes sour. Oxalic acid is present in spinach. As a result, spinach in an aqueous solution turns blue litmus into red.

Hence, the correct answer is C.