An ideal parallel-plate capacitor consists of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery that maintains a constant potential difference between the plates. If the separation between the plates is now doubled, the magnitude of the charge on the plates will

a. quadruple
b. double
c. third
d. fourth
e. half

e) half

Explanation:

as we know relation b/w charge(Q) , capacitance (C) and voltage (V) is

Q = CV (i)

we also know capacitance of a capacitor for separation d and area A is

C = ∈₀A/d (ii)

from  the above equation it is clear that C is inversely proportional to separation  if separation doubled  capacitance will reduced to half   and from equation first charge is directly proportional to capacitance.

that s why magnitude of charge will reduced to half  

so option (e) is right answer

frequency or wavelenth of em radiation in a vacuum