In this crossword puzzle (Fig 3.2), names of 11 elements are hidden. Symbols of these are given below. Complete the puzzle.

1. Cl 7. He

2. H 8. F

3. Ar 9. Kr

4. O 10. Rn

5. Xe 11. Ne

6. N

Fill in the blanks

(a) In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called ————

(b) A group of atoms carrying a fixed charge on them is called ————.

(c) The formula unit mass of Ca₃ (PO₄)₂ is ————.

(d) Formula of sodium carbonate is ——and that of ammonium sulphate is ————.

Complete the following crossword puzzle (Fig. 3.1) by using the name of the chemical elements. Use the data given

Across

2. The element used by Rutherford during his a–scattering experiment

3. An element which forms rust on exposure to moist air

5. A very reactive non–metal stored under water

7. Zinc metal when treated with dilute hydrochloric acid produces a gas of this element which when tested with burning splinter produces a pop sound

Down

1. A white lustrous metal used for making ornaments and which tends to get tarnished black in the presence of moist air

4. Both brass and bronze are alloys of the element

6. The metal which exists in the liquid state at room temperature

8. An element with symbol Pb

Identify the total number of inert gases, their names, and symbols from this cross-word puzzle.

Write the formulae for the following and calculate the molecular mass for each one of them.

(a) Caustic potash

(b) Baking powder

(c) Lime stone

(d) Caustic soda

(e) Ethanol

(f) Common salt