Why should a magnesium ribbon be cleaned before being burnt in air? 

Which type of reaction takes place when magnesium ribbon burns in the air? Why is it called so? 

Why is it suggested to wear dark coloured goggles while watching magnesium ribbon burning in the air? 

What happens when magnesium oxide dissolves in water? 

Solve the crossword puzzle. Hints are given below. 

Across

6. The substance which takes part in a chemical reaction. 

7. The substances that are formed as a result of a chemical reaction. 

9. Double displacement are _____ in nature. 

10. Only a single substance is formed as a result of _____ reaction. 

11. A brown substance with the chemical formula ${\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}$. 

12. Formation of nitric oxide from nitrogen and oxygen at $3000°\mathrm{C}$ is an example of _____ reaction. 

14. Obtained on heating ${\mathrm{CaCO}}_3$. 

15. BHT is an _____. 

Down

1. A chemical _____ is a symbolic representation of a chemical change. 

2. Digestion of food in our body is an example of _____ reaction.

4. A process that involves the gain of oxygen or the loss of hydrogen. 

5. A process that involves the gain of hydrogen or loss of oxygen. 

8. The oxidation of fats and oils in food results in an unpleasant smell and taste. 

13. A chemical equation that contains an equal number of atoms of each element on both sides of the equation.