To find the number of biggest square plates that can be obtained from a rectangular plate, we need to determine the maximum size of the square plates that can fit within the given rectangular plate.

Given:
Breadth of rectangular plate = 12 cm
Length of rectangular plate = 48 cm

Finding the side length of the square plate:
The side length of the square plate should be equal to the smaller dimension of the rectangular plate to ensure it can fit within the rectangular plate.

In this case, the breadth of the rectangular plate is smaller than the length. Therefore, the side length of the square plate will be 12 cm.

Calculating the number of square plates that can fit:
To find the number of square plates that can fit within the rectangular plate, we divide the length and breadth of the rectangular plate by the side length of the square plate.

Number of square plates in length = Length of rectangular plate / Side length of square plate
Number of square plates in length = 48 cm / 12 cm = 4

Number of square plates in breadth = Breadth of rectangular plate / Side length of square plate
Number of square plates in breadth = 12 cm / 12 cm = 1

To find the total number of square plates, we multiply the number of square plates in length by the number of square plates in breadth.

Total number of square plates = Number of square plates in length * Number of square plates in breadth
Total number of square plates = 4 * 1 = 4

Therefore, the correct answer is option C, 4 square plates can be obtained from the given rectangular plate.