Which of the following has the lowest enol content?

Write the structural formulas and names of the four possible aldol condensation products from propanal and butanal. In each case,indicate which aldehyde acts as the nucleophile and which acts as the electrophile.

The compound that $CANNOT$ be obtained from the aldol condensation reaction shown below, is

Fehling solution is

Product $A$ is

Identify the reagents $(1-4)$ required for the transformations shown and arrange them in the correct order.
$(1)$ $LiAlH_4$
$(2)$ $OsO_4$
$(3)$ $NaIO_4$
$(4)$ $NaBH_4$