As per Pauling, the radius of an isoelectronic ion in a given crystal is inversely proportional to the effective nuclear charge,
Z∗.
Z∗=Z−σ; where
σ represents the screening constant. The crystal structure of
NaF is shown as below :
![](https://s3-us-west-2.amazonaws.com/infinitestudent-images/ckeditor_assets/pictures/613277/original_original_original_3.png)
The radius of
F− in pm is
(130+x) . The value of
x in nearest possible integer is