An infinite number of charges each equal to 'q' are placed along the X-axis at $x=1$, $x=2$, $x=4$, $x=8$ ..... The potential at the point x = 0 due to this set of charges is

We know V due to charge q $=\frac{kQ}{r.}$
V is a scalar quantity
total potential at 0 is just sum of all charges.
$\therefore V=\frac{kq}{1}+\frac{kq}{2}+\frac{kq}{4}+----$
$=kq(\frac{1}{1-\frac{1}{2}})$ (sum of infinite $G.P=\frac{a}{1-r})$
$V=\frac{q}{4\pi {\epsilon }_0}2$
$\therefore V=\frac{2q}{4\pi {\epsilon }_0}$