How many stereoisomers does hexa-2,4-diene, CH3-CH=CH-CH=CH-CH3, have?

JEE Main levelSingle correct optionDifficulty 2 of 3st063

How many stereoisomers does hexa-2,4-diene, $CH X_{3} - CH = CH - CH = CH - CH X_{3}$ , have?

There are two double bonds, so

2^{2} = 4

combinations (E,E), (Z,Z), (E,Z) and (Z,E). The molecule is symmetric about its centre, so (E,Z) and (Z,E) are the same compound. The number is 3.