A: Fresnel diffraction occurs when the source of light or the screen or both are at a finite distances from the diffracting device
B: Diffracted light can be used to estimate the helical structure of nucleic acids.
A) A is true, B is false
B) Both A and B are true
C) A is false, B is true
D) Both A and B are false

Hint:The light undergoes diffraction which means deviation from its path due to the nature of the wave. The distances from the light source and the boundary and the boundary to the screen are two factors that affect the diffraction.

Complete step-by-step solution:
The diffraction can be explained by the Huygens principle. Each wave front consists of many secondary wavelets. The secondary wavelets which are obstructed during the propagation will also alter the amplitude and phase of other secondary wavelets. These interference patterns will cause diffraction to occur. The Fresnel diffraction occurs which is comparable to the size of obstruction. Unique diffraction patterns are formed when the distance from the source to the obstruction and distance from obstruction to screen is comparable to the size of obstruction.
The Fresnel diffraction is a near field effect in which the screen only is at a finite distance from the diffracting device. Thus the statement A is false. The nucleic acid is an optically active medium. We can pass polarized light through the nucleic acid. The wavelength of the polarization changes which helps to study the helical structure of nucleic acid.
And the polarized light is used to estimate the helical structure. Thus the statement B is true.
The answer is option C.

Note:- The medium can be left or right polarized. The refractive indices of the medium are diffract for both cases. And due to this the helical structure can be easily observed. And the Fresnel diffraction is different from the Fraunhofer diffraction due to its unique diffraction patterns.