The acid which is used in pickles is
Acetic acid
The table given below shows the acids and their usage:
AcidUsageAcetic AcidPickles and other food substancesCitric AcidFood preservation and in soft drinksSulphuric and Nitric AcidManufacture of chemical fertilizersSulphuric AcidAutomobile batteryTannic AcidProduction of ink and leather
The acid which is used in pickle is acetic acid whose common name is vinegar.