The compound A on treatment with Na gives B, and with PCl5 gives C. B and C react together to give diethyl ether. A, B, and C are in the order:

The compound A is ethanol C2H5OH. The compound A on treatment with Na gives sodium ethoxide (C2H5ONa) which is compound B.
C2H5OH + Na → C2H5ONa + 1/2H2
The compound A on treatment with PCl5 gives ethyl chloride (C2H5Cl) which is compound C.
C2H5OH + PCl5 → C2H5Cl + HCl + POCl3
B and C react together to give diethyl ether.
C2H5ONa + C2H5Cl → C2H5OC2H5 + NaCl