Matter in Our Surroundings — Science STD 9 — Question

Compute the number of ions present in 5.85g of sodium chloride.

Explain briefly, how gases can be liquefied.

Why is an atom neutral inspite of the presence of charged particles in it?

The atomic species A and B have different number of protons but the same number of nucleons. On the other hand, the atomic species X and Y have the same number of protons but different number of nucleons. Which pair is an example of isobars? Why?

The valencies (or charges) of some of the ions are given below:

Ion	Valency(Charges)	Ion	Valency(Charge)
Sodium ion	1+	Nitrate ion	1-
Copper ion	2+	Sulphide ion	2-

Using this information, write down the formulae of:

1. Sodium sulphide.
2. Copper nitrate.

Name the elements water is made of. What are the valencies of these elements? Work out the chemical formula for water.

What is the name of the clear liquid formed when a solid dissolves in a liquid?

Give reason for the following observation:
The smell of hot sizzling food reaches us even from a considerable distance but to get the smell form cold food, we have to go close to it.

The difference in the mass of 100 moles each of sodium atoms and sodium
ions is 5.48002g. Compute the mass of an electron.

Which of the following materials fall in the category of a “pure substance”?

1. Ice.
2. Milk.
3. Iron.
4. Hydrochloric acid.
5. Calcium oxide.
6. Mercury.
7. Brick.
8. Wood.
9. Air.