Dilute HCl is a stronger acid than concentrated H2CO3
Reason
HCl dissociates almost completely in aqueous solution and produces a high concentration of H+ ions and Cl– ions, hence is a strong acid. Whereas, H2CO3 is a weak acid because it dissociates partially yielding H+ ions and bicarbonate HCO3– ion and hence, contains ions as well as molecules. Therefore, dil. HCl is a stronger acid than conc. H2CO3.