Question

Every action has an equal opposite reaction . then why does it not work in fluids . And when we put some body in water why does it sink if this law is universal (or is it not universal )?

Answer 1

newtons 3rd law is equally valid in case of contact between solid and liquid.
it does not bounce back because of inelastic collision and viscous force between solid and liquid also gravitational force is downward so these two forces quickly pulls it downward to see the bounce back you might have to see the phenomena in slow motion.
you can put your hand quicly on water surface or jump your body horizontally on surface you will feel the force and skin may be damaged!which proves action reaction force.