Explanation:
When there is no change in chemical composition of a substance then it is known as physical change.
When we say that mass is conserved during a physical change then it means that total mass of the substance or object will remain the same from beginning till the end.
For example, a metal box of mass 20 grams is beaten with hammer. Its shape will change which is a physical change and after beaten with the hammer its mass still remains 20 grams.
Rubber. The other three are metals, and therefore good conductors.
Answer:

Explanation:
It is given that, a proton moves at constant velocity, through a region in which there is an electric field and a magnetic field such that,
The electric field is, E = 800 V/m
Magnetic field, B = 0.25 T
We know that the net force in the region of magnetic and electric field is given by Lorentz forces. But here, the proton moves with constant velocity. So, the net force acting on it is 0.
i.e.

Hence, this is the required solution.