The ionic radii of A+ and B− ions are 0.98×10−10m and 1.81×10−10m. The coordination number of each ion in AB is

Radius ratio, r+r−=0.98×10−101.81×10−10=0.541It lies in the range of 0.414 to 0.732 hence, coordination number of each ion will be 6 as the compound will have NaCl type structure i.e., octahedral arrangement.