Which of the following is Lindlar catalyst?

Lindlar catalyst is a heterogeneous catalyst that consists of palladium deposited on calcium carbonate (or barium sulfate), which is then treated (poisoned) with various forms of lead or quinoline to reduce its activity. It is commonly described as partially deactivated palladised charcoal.

Let us examine each option. Option (1), zinc chloride and HCl, is Lucas reagent used to distinguish between primary, secondary, and tertiary alcohols. Option (2), cold dilute $$KMnO_4$$ solution, is Baeyer's reagent used for the test of unsaturation. Option (3), sodium in liquid $$NH_3$$, is Birch reduction conditions used to reduce alkynes to trans-alkenes. Option (4), partially deactivated palladised charcoal, is the correct description of Lindlar catalyst, which is used to selectively reduce alkynes to cis-alkenes.

Hence, the correct answer is option (4).