What particle determines an atom’s identity and never changes?

Protons is one of the composite subatomic particles (particles that never changes) and it identifies an atom

500 N

Explanation:

From the question,

Sum of clockwise moment = sum of anti clockwise moment.

F×d = F'×d' Equation 1

Where F = Force applied to lift the load, d = distance, F' = Force required, d' = distance of the required force from the fulcrum

Make F' the subject of the equation

F' = F×d/d' Equation 2

Given: F = 1200 N, d = 25 cm, d' = 60cm.

Substitute these values into equation 2

F' = 1200×25/60

F' = 500 N.

Hence the force required to balance the load is 500 N