The correct order of radii is
N <Be <B
F-<O2-<N3-
Na< Li< K
Fe3+< Fe2+< Fe4+
B.
F-<O2-<N3-
These are isoelectronic species and their radii decreases with increasing their atomic number due to increasing effective nuclear charge (Zeff).
where, Zeff = effective nuclear charge, Z= atomic number and = screening constant. For F-, O2- and N3-, the value of is the constant due to equal number of electron. So order of Zeff is F > O2-> N3-, hence, order of radii is
KI and CusO4 solution when mixed, give :
CuI2 + K2SO4
Cu2I2 + K2SO4
K2SO4 + Cu2I2 + I2
K2SO4 + CuI2 + I2