Which of the following compounds does $\underline{\text{NOT}}$ contain phantom atoms?

Structures and $IUPAC$ names of some hydrocarbons are given below. Explain why the names given in the parentheses are incorrect.
$(a)$ $CH_3-CH(CH_3)-CH_2-CH_2-CH(CH_3)-CH(CH_3)-CH_2-CH_3$
Name: $2,5,6-$Trimethyloctane [and not $3,4,7-$Trimethyloctane]
$(b)$ $CH_3-CH_2-CH(CH_2CH_3)-CH_2-CH(CH_3)-CH_2-CH_3$
Name: $3-$Ethyl$-5-$methylheptane [and not $5-$Ethyl$-3-$methylheptane]

The $IUPAC$ name of neopentane is :-

The $IUPAC$ name of $CH_2=CH-CH(CH_3)_2$ is:

What is the chemical formula of the ethyl group represented as $CH_3CH_2$?

What is the $IUPAC$ name of $NC-CH_2-CH(CN)-CH_2-CN$?