Which of the following is unique for any given element?

The answer is could either be protons or the atomic number. I would go with the atomic number.

The number of protons equals the atomic number on the periodic table. Every atom of a particular element contains the same number of protons. Each element has a unique atomic number, or a unique number of protons in its nucleus.

I hope this helped.

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards