Why does the maximum packet lifetime have to be large enough to ensure that not only the packet but also its acknowledgments have disappeared?

Give one potential disadvantage when Nagle's algorithm is used on a badly congested network.

Give two examples of cases where TCP sends data$-$less packets on an established connection $($which is not being torn down$).$

Exercise $5\mathrm{.}0$ from section $12\mathrm{.}24$ of the textbook:

Suppose you see multiple TCP connections on your workstation in state FIN$\_$WAIT$\_1.$ What is likely going on$?$ Whose fault is it$?$

What might be going on if you see connections languishing in state FIN$\_$WAIT$\_2?$