Your answer to your question is: 1s² 2s² 2p⁶
I just took a test with this question and got the answer wrong for saying ethane. The correct answer is propane.
When a chemical reaction takes place it changes the composition of the reactants. The ways to tell if a reaction is occurring are,
1-Release of heat
2-Production of a gas
3-Formation of a precipitate
4-Change in color
10 atoms. If there are 10 in the reactants you need the same number in the products