(ii) To have a duck at each end, choose 2 ducks from the 3 available. This can be done in \(^3P_2\) ways. The remaining 8 positions can be filled with the 10 remaining ornaments (6 wooden animals and 4 sea-shells) in \(^10P_8\) ways. Therefore, the total number of arrangements is \(^3P_2 \times ^{10}P_8 = 10886400\).

(iii) Place a duck at each end, which can be done in \(^3P_2 = 6\) ways. The remaining 8 positions must alternate between wooden animals and sea-shells. Arrange the 4 sea-shells in \(^4P_4 = 24\) ways and the 4 wooden animals in \(^6P_4 = 360\) ways. Since the arrangement must alternate, swap the positions of sea-shells and wooden animals in 2 ways. Therefore, the total number of arrangements is \(6 \times 24 \times 360 \times 2 = 103680\).