The vector parts that add up to the resultant are called

"Components"

Explanation:

A vector pointing in a particular direction can always be decomposed into multiple vectors whose sum yields that vector. These vectors are referred to as components. Most frequently, vectors are decomposed into its components in the context of coordinate systems. For example an origin vector of length sqrt(2) pointing up 45 degrees in a (x,y) coordinate system has an x-component (1,0) and a y-component (0,1).

answer; /// i believe that the correct answer is (c)

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.