$A$ rectangular tank of depth $8 \, m$ is full of water $(\mu = 4/3)$. The bottom is seen at an apparent depth of:

Pick out the wrong statement from the following:

$A$ bird is flying $3\, m$ above the surface of water. If the bird is diving vertically down with speed $= 6\, m/s$,its apparent velocity as seen by a stationary fish underwater is $m/s$.

$A$ composite slab consisting of different media is placed in front of a concave mirror of radius of curvature $150 \, cm$. The whole arrangement is placed in water (refractive index $\mu = 4/3$). An object $O$ is placed at a distance $20 \, cm$ from the slab. The refractive indices of the different media are given in the diagram. Find the final image formed by the system.

$A$ glass slab of thickness $6.0 \text{ cm}$ is placed on a piece of paper on which an ink dot is marked. By how much distance would the ink dot appear to be raised (in $\text{ cm}$)? The velocity of light in glass is $2 \times 10^8 \text{ m/s}$ and that in air is $3 \times 10^8 \text{ m/s}$.

$A$ glass slab of thickness $4 \ cm$ contains the same number of waves as $5 \ cm$ of water when both are traversed by the same monochromatic ray of light. The refractive index of water is $4/3$. What is the refractive index of glass?