Which molecular formula does not exhibit chain isomerism?

Which of the following pairs of alkenes is an example of position isomers?

Esters are functional isomers of:

Given below are two statements :
Statement $(I) :$ $CH_3CH=CHCH_3$ and $cyclobutane$ are isomeric compounds.
Statement $(II) :$ $CH_3CH_2CH_2CH_2NH_2$ and $(CH_3CH_2)_2NH$ are functional group isomers.
In the light of the above statements,choose the correct answer from the options given below :

Which isomerism is exhibited by the functional group diethylamine?

Give the number of structural isomers for methane,ethane,propane,butane,pentane,hexane,heptane,and decane.