They are geometric isomers. Thus option C is the correct answer.
what is isomers ?
Two chemical species with the same number and types of atoms but different configuration are called as isomers, the spontaneous process by which isomers are formed called isomerization.
This process is independent of bond energy of the configurations.
Different types of isomers are structural isomers, geometric isomers, stereoisomers, optical isomers.
The major type called structural Isomers where atoms and functional groups are differently joined with each other. For example, 1-fluoropropane and 2-fluoropropane positional change.
Another types is stereoisomers formed between atoms and functional groups with differential geometrical positioning.
This class include enantiomers which are non-superimposable mirror images of each other and have chiral centers. example are D-threose and D-erythrose.
In stereoisomers, the class of diastereomers have different physical properties and reactivities.
Thus option C is the correct answer.
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