Which of the following processes involves the principle of electrostatic induction?

Three charges are placed as shown in the figure. The magnitude of $q_1$ is $2.00\, \mu C$,but its sign and the value of the charge $q_2$ are not known. Charge $q_3$ is $+4.00\, \mu C$,and the net force on $q_3$ is entirely in the negative $x-$ direction. As per the condition given,the signs of $q_1$ and $q_2$ will be

An inclined plane making an angle $30^{\circ}$ with the horizontal is placed in a uniform horizontal electric field of $100 \ Vm^{-1}$ as shown in the figure. $A$ small block of mass $1 \ kg$ and charge $0.01 \ C$ is allowed to slide down from rest from a height $h=1 \ m$. If the coefficient of friction is $0.2$,then the acceleration of the block is nearly,
(Acceleration due to gravity,$g=10 \ ms^{-2}$) (in $ms^{-2}$)

Two identical small spheres carry charges $Q_1$ and $Q_2$ $(Q_1 >> Q_2)$. The force between them is $F_1$. The spheres are brought into contact and then placed at the same distance. The new force between them is $F_2$. Then $F_1/F_2$ will be:

Five balls numbered $1$ to $5$ are suspended using separate threads. Pairs $(1,2), (2,4)$ and $(4,1)$ show electrostatic attraction while pairs $(2,3)$ and $(4,5)$ show repulsion. Therefore,ball $1$ must be:

Two charged particles,each of mass $3 \ g$ and charge $0.2 \ \mu C$,stay in (vacuum) equilibrium on a horizontal surface with a separation of $20 \ cm$. The coefficient of friction is $\left[\frac{1}{4 \pi \epsilon_0}=9 \times 10^9 \ Nm^2 C^{-2}\right]$ and $\left(g=10 \ ms^{-2}\right)$.