According to triangle law of forces, resultant of two forces must be greater than or equal to the third force.

In option ,
\(\mathrm{F}_1(3\mathrm{N}) + \mathrm{F}_2(1\mathrm{N})\) Hence, these sets of concurrent forces may not in equilibrium.
In option ,
F_1(3N) + F_2(5N) Hence, these sets of concurrent forces also may not in equilibrium.
In option ,

F_1(3N) + F_2(5N) > F_3(6N)

Hence, these sets of concurrent forces may be in equilibrium.
In option ,
F_1(3N) + F_2(5N) Hence, these sets of concurrent forces may not in equilibrium.