The correct option is B R=√3I
The resultant of two waves is given by R2=A2+B2+2ABcosθ;θ is the phase difference and A and B are the amplitudes of the individual waves.
Since both the waves are identical, their amplitudes are equal
Thus, R2=A2+A2+A2=3A2⟹R=√3A
Since intensity is proportional to √A, we can write the resultant amplitude R=√3I
The correct option is (b)