The compound is known by which of the following names?

What is the $IUPAC$ name of the compound $CH_3-CO-CH_2-CH(OH)-CHO$?

Give rules of nomenclature of organic compounds containing one or more functional groups.

What is the correct $IUPAC$ name for a molecule that has two amino groups $(-NH_2)$ in opposing $(para)$ locations around a benzene ring?

The $IUPAC$ name of the given compound is:

Fill in the blanks:
$(1)$ ....... model indicates only bonds in a molecule.
$(2)$ Only ......... model of a molecule indicates both bonds as well as atoms.
$(3)$ In the nomenclature of cyclic compounds,the ....... prefix is written before the name of the simple chain containing alkane.
$(4)$ The names of $C_{20}H_{42}$ and $C_{30}H_{62}$ are ........... and .......... respectively.