Figure shows tracks of three charged particles in a uniform electrostatic field. Which particle has the highest charge to mass ratio ?

Now, acceleration $\left(a\right)=\frac{F}{m}=\frac{Eq}{m}$

vertical displacement   $\left(h\right)=\frac{1}{2}a{t}^2=\frac{1}{2}\left(\frac{Eq}{m}\right)t^2$

$h\propto \frac{q}{m}$

Since the deflection of the particle 3 is more, its charge (q) to mass (m) ratio is more.