Since C = AEô/d
therefore, capacitance is proportional to area
as, the area increases capacitance also increases.

Parallel Plate Capacitor:
A parallel plate capacitor consists of two parallel conducting plates separated by a distance. It is used to store electrical energy in the form of an electric field between the plates.

Capacity of a Capacitor:
The capacity or capacitance of a capacitor is a measure of its ability to store electrical charge. It is defined as the ratio of the amount of charge stored on each plate to the potential difference between the plates.

Effect of Various Factors on Capacitance:
Let's examine the effect of the given factors on the capacitance of a parallel plate capacitor:

a) Area of the Plate is Decreased:
When the area of the plates is decreased, the capacitance of the capacitor decreases. This is because the amount of charge that can be stored on the plates decreases, resulting in a lower capacitance.

b) Distance Between the Plates Increases:
When the distance between the plates increases, the capacitance of the capacitor decreases. This is because the electric field between the plates becomes weaker, reducing the amount of charge that can be stored, and hence decreasing the capacitance.

c) Area of the Plate is Increased:
When the area of the plates is increased, the capacitance of the capacitor increases. This is because a larger plate area allows for more charge to be stored on the plates, resulting in a higher capacitance.

d) Dielectric Constant Decreases:
When the dielectric constant decreases, the capacitance of the capacitor decreases. The dielectric constant is a measure of the ability of a material to store electric charge. A lower dielectric constant means that the material between the plates is less effective at storing charge, resulting in a lower capacitance.

Conclusion:
From the above analysis, it is clear that the capacitance of a parallel plate capacitor increases when the area of the plates is increased. This is because a larger plate area allows for more charge to be stored on the plates, resulting in a higher capacitance. Therefore, the correct answer is option 'C'.