Answer:
Get narrower
Step-by-step explanation:
The equation of diffraction grating is given by :

Where
d is the slit width
m is the order
Also,

N is the number of slits of a diffraction grating
As the number of slits of a diffraction grating increases, the bright fringes observed on the viewing screen get narrower. Also, the intensity of fringe will increase. So, the correct option is (c).