What gas? Gas is an invisible form so I don't see how it would have a "defined structure".
Answer:
From the second law of motion:
F = ma
we are given that the force applied on the block is 20N and the block accelerates at an acceleration of 4 m/s/s
So, F= 20N and a = 4 m/s/s
Replacing the variables in the equation:
20 = 4* m
m = 20 / 4
m = 5 kg
Answer:
Magnetic force is equal to 
Explanation:
We have given electron is accelerated with a potential difference of 81700 volt.
Magnetic field B = 0.508 T
Angle between magnetic field and velocity 
Mass of electron 
Charge on electron 
By energy conservation.



Magnetic force on electron



Answer:
C. a small charged particle.
Explanation:
typically beta radiation emits an electron which is a small negativity charged particle.
hope it helps. :)