3. Write chemical formula for the following
(a) nitrogen
(b) aluminium

Nitrogen:N2

Aluminum:Al

Explanation:

Nitrogen:The chemical formula for nitrogen gas is N2. The formula can be represented as N≡N.

Aluminum: Aluminum is a silvery-white metal which is extremely soft by nature. Totally earth's crust contains 8% of Aluminum.

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a.N

b.Al

Explanation:

nitogen is N in upper case and aluminium is Al.always the second letter is lower case

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

a:

by the combination of an unlimited number of elements