The alkyne shown is first reduced with Na in liquid $\mathrm{NH}{}_3$ and the product is then oxidised with PCC in $\mathrm{CH}{}_2\mathrm{Cl}{}_2$. Which structure is the final product?

The compound is hex-4-yn-1-ol. Na/$\mathrm{NH}{}_3$ reduces the internal alkyne to the trans alkene, (E)-hex-4-en-1-ol, and the alcohol is untouched. PCC then stops the primary alcohol at the aldehyde, giving (E)-hex-4-enal. The Z isomer would come from Lindlar and the acid from Jones oxidation.