(a) From the relation `r prop A^(1//3)` ,
We have `(r_2)/(r_1) = ((A_2)/(A-1))^(1//3)`
or ` ((A_2)/(4))^(1//3) ` (14(^(1//3)
:. `A_2 =56`
(b) `Z_2 = A_2 ` number of neutrons
`=56 - 30 =26`
`:. F = Rc(Z-1)^2 ((1)/(1^2) - (1)/(2^2)) = (3Rc)/(4) (Z-1)^2`
Substituting the given values of R, c and Z, we get
` f= 1.55xx10^18 Hz`