To find the weight percentage of oxygen (W(O)) in the aldehyde (RCOH), we can use the fact that the sum of the weight percentages of all elements in a compound must add up to 100%.

Given:
W(C) = 54.5%
W(H) = 9.1%

Let W(O) be the weight percentage of oxygen.
Since there are no other elements given besides carbon (C), hydrogen (H), and oxygen (O) in the aldehyde, we can write:

W(C) + W(H) + W(O) = 100%
54.5% + 9.1% + W(O) = 100%
63.6% + W(O) = 100%
W(O) = 100% - 63.6%
W(O) = 36.4%

Therefore, the weight percentage of oxygen (W(O)) in the aldehyde is 36.4%.