The correct option is A 3.72 pm
CsBr has a bcc type structure. Here Cs+ ion are present at the body centre of the cube and Br− ions are present at the corners of the cube. So the relation between inter ionic distance (r++r−) and edge length will be
√3a=2(r++r−)
Shortest distance would be r++r−
Here, r++r−=√3a2=1.73×4.32=3.7195 pm≈3.72 pm