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 NaCltype structure i.e., octahedral arrangement.