Three forces acting on a body are shown in the figure. To have the resultant force only along the $y-$ direction, the magnitude of the minimum additional force needed is

The correct option is C $0.5\text{N}$
Given that the resultant force should be along $y$ direction only, so the $F_{net}$ along $x$ direction should be zero.

Taking $x-$components of all $3$ forces given in diagram and $1$ additional force, the total force should be zero.

Let $f$ be the magnitude of minimum force which must be along $x$ direction, by resolving the vectors we get,

$1\times \cos {60}^{\circ }+2\sin {30}^{\circ }+f-4\sin {30}^{\circ }=0$

$\therefore f=0.5\text{N}$

Hence, option $\left(\text{C}\right)$ is the correct answer.