Two particles of masses 1 gm and 2 gm are kept at a separation l. Moment of inertia of the system is minimum about the axis AB and it has a value of $\frac{98}{3}gm-c{m}^2$. Then separation between the particles is 

If l be the separation between the particles, then distance of centre of mass of the system from 1 gm is $\frac{2\times l}{1+2}=\raisebox{1ex}{$l$}\!\left/ \!\raisebox{-1ex}{$3$}\right.$. Since moment of inertia of the system about line AB is minimum, line AB must pass through the centre of mass. 

$\therefore 1\times {\left(\frac{2l}{3}\right)}^2+2\times {\left(\frac{l}{3}\right)}^2=\frac{98}{3}\Rightarrow l=7cm$