What should be the equal charge on helium-filled balloons as shown in the figure?

Two identical simple pendulums each of length $L = 5 \, cm$ are suspended from the same support. When the bobs are given an equal charge of $q = 2 \, \mu C$ each, the distance between the bobs becomes $d = 6 \, cm$. Find the mass $m$ of each bob. (Take $g = 10 \, m/s^2$ and $k = 9 \times 10^9 \, N \cdot m^2/C^2$). (in $ \, kg$)

Two charges $q$ and $-3q$ are placed fixed on the $x$-axis separated by a distance $d$. Where should a third charge $2q$ be placed such that it will not experience any force?

$A$ charge $Q$ is to be divided between two objects. The values of the charges on the objects so that the electrostatic force between them will be maximum is

$A$ particle of mass $M$ and charge $q$ is placed at the midpoint between two fixed charges each of magnitude $Q$, separated by a distance $2d$. The system is collinear as shown in the figure. If the particle is displaced by a small distance $x$ $(x \ll d)$ along the line joining the two charges and released, it will oscillate about the mean position with a time period $T$. ($\varepsilon_{0}$ is the permittivity of free space)

An infinite number of point charges,each carrying $1 \,\mu C$ charge,are placed along the y-axis at $y=1 \,m, 2 \,m, 4 \,m, 8 \,m, \ldots$. The total force on a $1 \,C$ point charge,placed at the origin,is $x \times 10^{3} \,N$. The value of $x$,to the nearest integer,is .........
[Take $\frac{1}{4 \pi \epsilon_{0}}=9 \times 10^{9} \,N m^{2}/C^{2}$]