Question

what is the condition for an object to sink in water? what is the physical meaning of relative density? what do hydrogen filled balloon float in air?

Answer 1

An object sinks in water because the weight of the object is greater than the buoyant force of the water.

Relative density = density of the substance/ density of water

Hydrogen is lighter than air infact its the most lightest gas of all even lighter then helium but we use helium in balloons because  its harmless when hydrogen is extremely flameable

Answer 2

An object sinks in water when the weight of the object is greater than the buoyant force exerted by the water.

Relative density = density of the substance/ density of water

Hydrogen is a lighter gas , so hydrogen filled ballon float in air.....