Assertion: For best contrast between maxima and minima in the interference pattern of Young's double slit experiment, the intensity of light emerging out of the two slits should be equal.

Reason: The intensity of interference pattern is proportional to square of amplitude.

Assertion: The clouds in sky generally appear to be whitish.

Reason: Diffraction due to clouds is efficient in equal measure at all wavelengths.

Assertion: Crystalline solids can cause X-rays to diffract.

Reason: Interatomic distance in crystalline solids is of the order of 0.1 nm.

Assertion: At the first glance, the top surface of the Morpho butterfly's wing appears a beautiful blue green, if the wind moves the colour changes.

Reason: Different pigments in the wing reflect light at different angles.

Assertion: In Young's double slit experiment the two slits are at distance d apart. Interference pattern is observed on a screen at distance D from the slits, a dark fringe is observed. Then, the wavelength of wave is proportional to square of distance of two slits.

Reason: For a dark fringe, intensity is zero.

Assertion: A double convex lens $\left(\mu =1.5\right)$ has focal length 10 cm. When the lens is immersed in water $\left(\mu =\raisebox{1ex}{$4$}\!\left/ \!\raisebox{-1ex}{$3$}\right.\right)$ its focal length becomes 20 cm.

Reason: $\frac{1}{f} = \frac{{\mu }_1-{\mu }_m}{{\mu }_m}\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$

Assertion: Owls can move freely during night.

Reason: They have large number of rods on their retina.

Assertion: In optical fibre, the diameter of the core is kept small.

Reason: This smaller diameter of the core ensures that the fibre should have incident angle more than critical angle required for total internal reflection.

Assertion: The formula connecting u, v and f for a spherical mirror is valid only for mirrors whose sizes are very small compared to their radii of curvature.

Reason: Laws of reflection are strictly valid for plane surfaces, but not for large spherical mirrors. 

Assertion: The colour of the green flower seen through red glass appears to be dark.

Reason: Red glass transmits only red light.