Which pairs are isomers? ch3ch2ch2ch3 and ch3ch(ch3)ch2ch3. ch3ch(ch3)ch2ch2ch2ch2ch2ch2ch3 and ch3ch2ch2ch2ch(ch2ch2ch3)ch2ch3. ch3ch2ch2ch2ch2ch3 and ch3ch2ch(ch3)ch2ch2ch3. ch3ch(ch3)ch2ch2ch(ch3)ch3 and ch3ch2ch2ch2ch2ch2ch2ch3. ch3ch(ch3)ch2ch3 and ch3ch2ch2ch2ch3.

1) ch3ch(ch3)2(iso butane) and ch3(ch2)2ch3 (normal butane) are structural isomers (more specifically show chain isomerism) 

2) ch3ch(ch3)(ch2)6ch3 and ch3(ch2)4ch(ch2ch2ch3)ch2ch3 are structural isomers (more specifically show chain isomerism) 

3) two are structural isomers (more specifically show chain isomerism) 

4) these two are not isomers 

5)these two are not isomers

The correct answer is "atomic weight".