A

To calculate the induced emf (E) in a coil of increasing radius in a uniform magnetic field, we use Faraday's law of electromagnetic induction. According to Faraday's law:
E = -rac{d heta}{dt}, where B8 is the magnetic flux. The magnetic flux (B8) through the coil is given by:
B8 = B imes A, where A is the area of the coil.
The area A of a circular coil with radius r is A = C0 r^2. Therefore,
B8 = B imes C0 r^2.
The changing radius r with respect to time t leads to the changing area A, given by rac{dA}{dt} = rac{d(C0 r^2)}{dt} = 2C0 r rac{dr}{dt}.
Applying Faraday's law gives us:
E = -B imes 2C0 r rac{dr}{dt}.
Since the induced emf is proportional to the rate of change of the area as radius increases. Thus the graph representation for this situation would be a direct proportionality indicating a positive slope as seen in Option A.