Answer:
B).
![F_N - mgcos\theta = 0](https://img.qammunity.org/2020/formulas/physics/middle-school/83yvvlrn61gk454f1f8ptpm85s1gj6s5q2.png)
Step-by-step explanation:
As we know that the force on the mass "m" which slides along the inclined plane is along the inclined surface
So it must have accelerated along that surface only
So we can write the equation for force along the inclined plane as
![F_(net) = ma](https://img.qammunity.org/2020/formulas/physics/high-school/ndgotbvij7522nqvxesuhb8y0a7dz9lzlt.png)
now if we wish to find net force perpendicular to the plane then we can say that it must be zero
Because perpendicular to the plane the net force on the given mass must be zero as it is not accelerating along that direction
So here we can say
![F_(net) = 0](https://img.qammunity.org/2020/formulas/physics/middle-school/9q4p9u2revacjd8j5kbcfyhz2q6ezl0w4u.png)
so we have
![F_N - mgcos\theta = 0](https://img.qammunity.org/2020/formulas/physics/middle-school/83yvvlrn61gk454f1f8ptpm85s1gj6s5q2.png)