Select the correct $IUPAC$ name of pyrogallol.

Which of the following $IUPAC$ names is incorrect?

Provide the $IUPAC$ name for the following compound:
$\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,H\,\,\,\,\,{C_4}{H_9}} \\
{\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,\,\,|} \\
{CH_3CH_2 - C - C - CH_3} \\
{\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,\,\,|} \\
{\,\,\,\,\,\,\,\,\,CH_3\,\,\,\,CH_3}
\end{array}$

Identify the compound that does not correctly match with its common name.

$A$. $HCHO$	Formaldehyde
$B$. $C_6H_5NH_2$	Aniline
$C$. $CH_3CH(CH_3)CH_3$	$n-$Butane
$D$. $CH_3CH(OH)COOH$	Lactic acid

According to the $IUPAC$ system,the given compound is named as:

The structure of $4-$Methylpent$-2-$enal is: