Is Matter Around Us Pure — Science STD 9 — Question

What do you understand by the tern "electronic configuration" of an element? Write down the electronic configuration of oxygen (At. No. = 8).

Describe a method to separate a mixture of camphor and sand.

What is the number of valence electrons in:

1. Sodium ion, Na⁺
2. Oxide ion, O^2-

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.

Explain why, hydrogen and oxygen are considered elements whereas water is not considered an element.

What is meant by a chemical formula? Write the formulae of one element and one compound.

What are radioactive isotopes? Give two examples of radioactive isotopes

What is Brownian motion? Draw a diagram to show the movement of a particle (like a pollen grain) during Brownian motion.

What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?

How formula unit mass is different from molecular mass?