In first case,
The capacitance of the capacitor with air as medium is given by
C1 = \(\frac{ɛ_oA}{d}\) = 8 pF ........................(i)
In 2nd case
The distance is reduced to half i.e. d/2 and K = 5.
So C2 = \(\frac{Kɛ_oA}{d/2} = 2K(\frac{ɛ_oA}{d})\)
Using Eq. (i) we get
C2 = 2K x 8 = 2 x 5 x 8 = 80 pF.