The correct option is C h decreases.
(a) When coin falls into water, block rises up since total weight i.e. block and coin decreases and upthrust remains almost same as the volume displaced by coin is comparatively small and
∴ l decreases
(b) When the coin falls in water, volume of water displaced by coin is equal to the volume of coin V1 (say).
When coin is at the top of wooden block, it displaces volume of water (V2), Which is more than V1, because weight of coin = weight of volume of water displaced by coin
or ρcV1g=ρlV2g⇒V2V1=ρcρl
∴ρc>ρl
∴V2>V1
Hence h decreases.
Final Answer: (a), (b)