Why Coulomb’s law is associated with Newton’s $3^{rd}$ law ?

Four charges equal to $-Q$ are placed at the four corners of a square and a charge $q$ is at its centre. If the system is in equilibrium the value of $q$ is

A point charge $q_1$ exerts an electric force on a second point charge $q_2$. If third charge $q_3$ is brought near, the electric force of $q_1$ exerted on $q_2$

Two identical conducting spheres with negligible volume have $2.1\, nC$ and $-0.1\, nC$ charges, respectively. They are brought into contact and then separated by a distance of $0.5 \,m$. The electrostatic force acting between the spheres is $.......... \, \times 10^{-9} \,N$

[Given : $4 \pi \varepsilon_{0}=\frac{1}{9 \times 10^{9}} SI$ unit]

Two equal negative charges are fixed at the points $ [0, a ]$ and $[0, -a]$ on the $y-$ axis. A positive charge $Q$ is released from rest at the points $[2a, 0]$ on the $x-$axis . The charge $Q$ will

Three point charges $q,-2 q$ and $2 q$ are placed on $x$-axis at a distance $x=0, x=\frac{3}{4} R$ and $x=R$ respectively from origin as shown. If $q =2 \times 10^{-6}\,C$ and $R =2\,cm$, the magnitude of net force experienced by the charge $-2 q$ is .......... $N$