The figure shows the tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge-to-mass ratio?

(N/A) Opposite charges attract each other,and like charges repel each other.
It can be observed that particles $1$ and $2$ both move towards the positively charged plate and are repelled away from the negatively charged plate.
Hence,these two particles are negatively charged.
It can also be observed that particle $3$ moves towards the negatively charged plate and is repelled away from the positively charged plate.
Hence,particle $3$ is positively charged.
The deflection $y$ of a charged particle in a uniform electric field $E$ after traveling a horizontal distance $x$ is given by $y = \frac{qEx^2}{2mv^2}$,where $q$ is the charge,$m$ is the mass,and $v$ is the initial velocity.
For a given velocity and horizontal distance,the deflection $y$ is directly proportional to the charge-to-mass ratio $(q/m)$.
Since particle $3$ shows the maximum deflection,it has the highest charge-to-mass ratio.