Identify the name of the method used for the three-dimensional representation of the molecule as follows:

$(i)$ Number of geometrical isomers for the given structure $X$:
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$(ii)$ Number of cyclic structural isomers with molecular formula $C_5H_{10} = Y$
$(iii)$ Number of ethers with molecular formula $C_4H_{10}O = Z$
Find the value of $X + Y + Z$.

Which of the following contains a plane of symmetry?

Identify $B$ in the following tautomerization reaction:
$4\text{-pyridone} \xrightarrow{KOH} B$

The product of this reaction should be

Examine the following three pairs of possible isomers. Now state whether the pairs represent identical compounds or different isomers.