The Fundamental Unit of Life — Science STD 9 — Question

A student placed a gas jar containing air in the upside down position over a gas jar full of red-brown bromine vapours. He observed that the red brown colour spread upwards into the jar containing air. Based on this observation, the student concluded that it is only the bromine vapour which moves up and diffuses into air in the upper jar, the air from the upper jar does not move down by diffusion into the lower jar containing bromine vapours. Do you agree with this conclusion of the student? Give reason for your answer.

Define ‘molecular mass’ of a substance.

Give reason for the following observations.
Naphthalene balls disappear with time without leaving any solid.

A large truck and a car, both moving with a velocity of magnitude u, have a head on collision and both of them come to a half after that. If the collision lasts for.
What vehicle experiences the greater force of impact?

State an important characteristic of uniform circular motion. Name the force which brings about uniform circular motion.

20g silver nitrate solution is added to 20g of sodium chloride solution. What change in mass do you expect after the reaction and why?