Write structures for each of the following compounds. Why are the given names incorrect? Write correct $IUPAC$ names.
$(i)$ $2-Ethylpentane$
$(ii)$ $5-Ethyl-3-methylheptane$

(N/A) $(i)$ The structure of $2-Ethylpentane$ is $CH_3-CH(C_2H_5)-CH_2-CH_2-CH_3$. The longest chain contains $6$ carbon atoms,not $5$. Therefore,the correct $IUPAC$ name is $3-Methylhexane$.
$(ii)$ The structure of $5-Ethyl-3-methylheptane$ is $CH_3-CH_2-CH(CH_3)-CH_2-CH(C_2H_5)-CH_2-CH_3$. According to the lowest locant rule,numbering should start from the end that gives the lower number to the substituent. Therefore,the correct $IUPAC$ name is $3-Ethyl-5-methylheptane$.