Answer :
force of gravitation between two different masses is given by
[tex]F = \frac{Gm_1m_2}{r^2}[/tex]
here in first case we will have
[tex]F_1 = \frac{G(1kg)(2kg)}{(1m)^2}[/tex]
[tex]F_1 = 2G [/tex]Newton
another case we have
[tex]F_2 = \frac{G(1kg)(2kg)}{(2m)^2}[/tex]
[tex]F_2 = \frac{G}{2} [/tex]Newton
another case we have
[tex]F_3 =\frac{G(2kg)(2kg)}{(1m)^2}[/tex]
[tex]F_3 = 4G [/tex]Newton
so the force will be maximum in last case when two 2 kg mass is placed at 1 m distance and minimum force is in second case when 1kg and 2kg mass is placed at 2 m distance