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Drawing FBD of 2kg blocks

Friction will act in leftward direction, as force ${\mathrm{F}}_1$ is applied in rightward direction. Drawing FBD of 4kg blocks:

Friction exerted by 2kg block, ${\mathrm{f}}_1$ on 4kg blocks will be in rightward direction (action - reaction pair). and the friction ${\mathrm{f}}_2$ applied by ground will also be in rightward direction, as ${\mathrm{F}}_2$ force is applied in left direction. Hence options (A) is correct.