Which of the following molecules or ions is polar?

Explanation:

1) Carbonate ions( ) is a polar molecule.Polarity of this ion is due to presence of three electro-negative oxygen atoms which will attract shared pair of electrons towards itself which will create negatively charged pole on oxygen and will also induce positively charged pole on carbon atom.

2) Hydrogen cyanide(HCN) is also polar molecule. Polarity of this ion is due to presence of electro-negative nitrogen atom which is bonded to carbon atom  will attract the shared pair of electrons towards itself which will create negatively charged pole on nitrogen atom and will induce positively charged pole on carbon atom.

3) Nitrate ion () is a polar molecule.Polarity of this ion is due to presence of three oxygen atoms. Oxygen is more electro-negative atom than the nitrogen atom which will attract shared pair of electrons towards itself which will create negatively charged pole on oxygen and will also induce positively charged pole on nitrogen atom.

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.

it would be a gas formation