Answer
a). If they are in series,
$\frac{1}{C_{s}}=\frac{1}{C}+\frac{1}{C}+.......... N \,\,times=\frac{N}{C}$
Thus, $C_{s}=\frac{C}{N}$
b). If they are connected in parallel,
$C_{p}=C+C+............ N\,\, times=NC$
c). Here if $C_{s}$ is equivalent of half of the capacitors, then
$\frac{1}{C_{s}}=\frac{1}{C}+\frac{1}{C}+........ \frac{N}{2}\,\, times=\frac{N}{2C}$
Thus, $C_{s}=\frac{2C}{N}$
Hence, total equivalent = $C_{p}=C_{s}+C_{s}=\frac{4C}{N}$
Work Step by Step
a). If they are in series,
$\frac{1}{C_{s}}=\frac{1}{C}+\frac{1}{C}+.......... N \,\,times=\frac{N}{C}$
Thus, $C_{s}=\frac{C}{N}$
b). If they are connected in parallel,
$C_{p}=C+C+............ N\,\, times=NC$
c). Here if $C_{s}$ is equivalent of half of the capacitors, then
$\frac{1}{C_{s}}=\frac{1}{C}+\frac{1}{C}+........ \frac{N}{2}\,\, times=\frac{N}{2C}$
Thus, $C_{s}=\frac{2C}{N}$
Hence, total equivalent = $C_{p}=C_{s}+C_{s}=\frac{4C}{N}$