Answer:
In given structure of substituted cyclohexane select the "Bromine" atom as the answer.
Explanation:
1,3-Diaxial Interactions:
As cleared from name, this type of interactions are found in cyclic alkanes in which one group present at position 1 (assumed number) experiences steric hindrance due to another group present at position 3.
Also, it is necessary that both the groups must be occupying either axial or equatorial positions respectively. For example, in given structure the methyl group at position 1 is at axial position and another bulky group which should interact with this methyl group must occupy axial position at carbon 3 next to carbon 1. Hence, as shown in figure, the Bromine atom is present at third carbon and is at axial position too.
In attached picture, the green lines indicate steric interactions between Methyl group and Bromine atoms which are involved in steric interactions in 1,3-diaxial fashion.
