Which of the following is the correct $IUPAC$ name of catechol?

What is the correct $IUPAC$ name of the following structure? Explain.
$CH_3-CH_2-CH(CH_2-CH_3)-CH_2-CH_2-CH(CH_3)-CH_2-CH_3$
$(i)$ $3-$ethyl$-6-$methyloctane
$(ii)$ $3-$methyl$-6-$ethyloctane
$(iii)$ $6-$methyl$-3-$ethyloctane

The suffix of the principal group,the prefixes for the other groups and the name of the parent in the structure $HO-CH_2-CH(CH_3)-CH=C(Cl)-CH_2-C(=O)-C(=O)OH$ are:

The $IUPAC$ name of $CH_3-COO-CH_2-COOH$ is:

What is the $IUPAC$ name of the compound $CH_3-CH(CH_3)-CH_2-CH_2-Cl$?

The $IUPAC$ name of the compound shown below is:
$H_2C-CH-CH_3$ (with an oxygen atom bridging the first two carbons)