Dilute hydrochloric acid is added to solid sodium carbonate. It is observed that:
A.No change takes place
B.A loud sound is produced
C.A brisk effervescence occurs
D.The solution turns blue

Hint:
If in the reaction of carbon dioxide, it shows brisk effervescence. Carbon dioxide gas is released as effervescence or bubbles. Metal carbonate and bicarbonate gets decomposed rarely with help of mineral acids with the evolution of carbon dioxide $C{O_2}$.

Complete step by step answer:
-Sodium carbonate is a chemical compound with a molecular formula $N{a_2}C{O_3}$. The aqueous solution of sodium carbonate is a strong base. Sodium carbonate is a stable but hygroscopic solid. It forms weakly acidic carbonic acid and a strong base, sodium hydroxide.
-The reaction of hydrochloric acid ($HCl$) and sodium carbonate ($N{a_2}C{O_3}$) yields a product of water (${H_2}O$), carbon dioxide gas ($C{O_2}$), and table salt ($NaCl$). In this reaction, intermediate carbonic acid (${H_2}C{O_3}$) formed, due to its unstable nature, it breaks down into water, carbon dioxide, and salt.
-The changes depend on the amount of $HCl$ and $N{a_2}C{O_3}$ added together because the complete neutralism of $N{a_2}C{O_3}$ with $HCl$ happens in two separate stages.
-In this reaction, sodium carbonate contains $N{a^ + }$ and ${(C{O_3})^{2 - }}$ ions. Carbonate ions use their oxygen lone pairs to pick up protons, which $HCl$ can react in the form of ${H_3}{O^ + }$.
$2{H_3}{O^ + } + {(C{O_3})^{2 - }} \to {H_2}C{O_3}$
${H_2}C{O_3}$ (Carbonic acid) is unstable and it will break down into $C{O_2}$ and ${H_2}O$ .
 ${H_2}C{O_3} \to {H_2}O + C{O_2}$
-Then in the reaction remaining $N{a^ + }$ ions reacts with $C{l^ - }$ and forms $NaCl$ .
 $N{a_2}C{O_3} + 2HCl \to 2NaCl + C{O_2} + {H_2}O$
-When hydrochloric acid is added to sodium carbonate, $C{O_2}$ occurs, along with the formation of sodium chloride and water.
-This reaction $C{O_2}$ is formed and it shows brisk effervescence.
Thus the correct answer is (C).

Note:The ratio of the elements present in the compound can be known by the chemical formula of an ionic compound or a covalent compound. The valency of an atom or ion is the number of electrons it shares, losses, or gains during a chemical reaction to attain stability that is the number of bonds it forms with the other atoms.