Question

a plastic tube is released in water will it sink or come to the surface of water

Answer 1

"It is a common property of water that it allows materials with higher density in it to sink and with lesser density to float.

Plastic has a density lesser than water and thus the force of buoyancy on plastic will be more than its force, throwing it in the upward direction.

The plastic tube will therefore come to the surface of water.

"

Answer 2

ANSWER:

When a plastic tube is released in water, it comes to the surface of the water.

EXPLANATION:  

Water has density of about $1 \mathrm{g} / \mathrm{cm}^{3}$ whereas plastic tube has density of about $0.92 \mathrm{g} / \mathrm{cm}^{3}$.

This low density of plastic tube is because of its less tightly packed molecules and less crystallinity. And Because of the low density that the plastic tube possess than water, makes the plastic tube come to the water surface.