Correct Answer - C
NaCl has face-centred cubic arrangement of `Cl^-` ions and `Na^+` ions are present in the octahedral voids. Hence, for such a solid radius of cation =0.414 x radius of the anion ( or `r_+/r_(-)`=0.414)
i.e., `r_+= 0.414xxr_(-)`
or `r_(-)=r_+/0.414=100/0.414`=241.5 pm