What is the net force on a $Cl^{-}$ placed at the centre of the bcc structure of $CsCl$

Three charges $ - {q_1},\,\, + {q_2}$ and $ - {q_3}$ are placed as shown in the figure. The $x$-component of the force on $ - {q_1}$ is proportional to

Out of gravitational, electromagnetic, Vander Waals, electrostatic and nuclear forces; which two are able to provide an attractive force between two neutrons

Two charges $-\mathrm{q}$ each are fixed separated by distance $2\mathrm{d}$. A third charge $\mathrm{d}$ of mass $m$ placed at the midpoint is displaced slightly by $x (x \,<\,<\, d)$ perpendicular to the line joining the two fixed charged as shown in figure. Show that $\mathrm{q}$ will perform simple harmonic oscillation of time period.  $T =\left[\frac{8 \pi^{3} \epsilon_{0} m d^{3}}{q^{2}}\right]^{1 / 2}$

Charges $4Q$, $q$ and $Q$ and placed along $x$-axis at positions $x = 0,x = l/2$ and $x = l$, respectively. Find the value of $q$ so that force on charge $Q$ is zero

Three charges $+Q, q, +Q$ are placed respectively, at distance, $0, \frac d2$ and $d$ from the origin, on the $x-$ axis. If the net force experienced by $+Q$, placed at $x = 0$, is zero, then value of $q$ is