What is the basic idea for solving this...??! How do we check these options?!
6. In Young's double-slit experiment. the separation
between the two slits is d and the wavelength of the light
is  $\lambda$.The intensity of light falling on slit 1 is four times
the intensity of light falling on slit 2. Choose the correct
choice(s).  (IIT-JEE, 2008)
a. If d= $\lambda$, the screen will contain only one maximum
b. If $\lambda <d<2\lambda$, atleast one more maximum (besides the
central maximum) will be observed on the screen
c. If the intensity of light falling on slit 1 is reduced so
that it becomes equal to that of slit 2. the intensities of
the observed dark and bright fringes will increase
d. If the intensity of light falling on slit 2 is increased so
that it becomes equal to that of slit I , the intensities of
the observed dark and bright fringes will increase