Answer: (i) \(18\). (ii) \(24\). (iii) \(48\).

For part (i), choose the chairperson from the three men in \(3\) ways.

Then choose the treasurer from the remaining two men in \(2\) ways.

After those two positions are filled, there are \(3\) people left who could be secretary.

So the number of ways is

\(3\times2\times3=\boxed{18}.\)

For part (ii), David is fixed in the middle seat. The other four people can be arranged in

\(4!=\boxed{24}\)

ways.

For part (iii), treat Alice and Carl as one block. This gives \(4\) objects to arrange: the block, Betty, David, and Ed.

These can be arranged in \(4!\) ways, and Alice and Carl can swap positions within the block in \(2\) ways.

Therefore the number of arrangements is

\(2\times4!=2\times24=\boxed{48}.\)