An isomer of ethanol is

Question

$\begin{array}{1 1} methanol \\ diethyl ether \\ acetone \\ dimethyl ether \end{array} $

Comments

How can methanol an isomer of ethanal? The structural formula of Ethanal is ch3cho with 2 carbons, whereas the structural formula of Methanol is ch3oh with only 1 carbon. So both- methanol and Ethanal differs from each other in structural formula.

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Thanks for the correction.