An element X has a valency 1.

(i) Write the chemical formula of its phosphide.

(ii) Write the chemical formula of its chloride.

(iii) Is element X a metal or a non-metal?

In a chemical compound calcium sulphate:

(i) Identify the two ions.

(ii) Write the chemical formula of compound formed when positive ion is replaced by sodium ion.

(iii) Name the resulting compound.

(i) Calculate the formula unit mass of Na₂CO₃.

[given atomic mass of Na = 23 u, C = 12 u and O = 16 u]

(ii) What is the mass of one mole of oxygen atoms?

(iii) Convert 12g of oxygen gas into mole, if atomic mass of oxygen is 16 u.

You are asked by your teacher to buy 10 moles of distilled water from a shop where small bottles each containing 20 g of such water are available. How many bottles will you buy?

State the two important laws of chemical combination. How Dalton’s atomic theory explains the two Laws?