Explanation:
The radius of a nucleus is given by the relation, \(r = {r_0}{(A)^{1/3}}\)
where, \({r_0} = \) constant
For \(O{s^{189}},{A_1} = 189,{r_1} = r\)
Thus,using \({r_2} = \frac{r}{3}\), we know that,
\(\frac{{{r_1}}}{{{r_2}}} = {\left( {\frac{{{A_1}}}{{{A_2}}}} \right)^{1/3}} \Rightarrow 3 = {\left( {\frac{{189}}{{{A_2}}}} \right)^{1/3}}\)
\( \Rightarrow 27 = \frac{{189}}{{{A_2}}} \Rightarrow {A_2} = 7\)
Thus, the answer is \(L{i^7}\)