Answer : The structure are shown below and the number of stereoisomers are possible in 3,5-dimethylnonane and 3,7-dimethyle-5-ethyldecane are 4 and 8 respectively.
Explanation :
Chiral carbon : It is carbon which is attached to the different types of atoms or molecules.
The number of stereoisomers possible for a compound is related to the number of chiral centers (n) present in it as,
where,
'n' is the number of chiral carbon present in the compound.
The number of chiral carbon present in 3,5-dimethylnonane is, 2 that means n = 2 (carbon-3 and carbon-5)
The number of stereoisomers are possible in 3,5-dimethylnonane is, 4
The number of chiral carbon present in 3,7-dimethyle-5-ethyldecane is, 3 that means n = 3 (carbon-3, carbon-5 and carbon-7)
The number of stereoisomers are possible in 3,7-dimethyle-5-ethyldecane is, 8