What atom should be balanced last when balancing hydrocarbon combustion reactions?
A. The oxygen atoms
B. The carbon atoms
C. Any of the three
D. The hydrogen atoms

A. The oxygen atoms

Explanation:

A hydrocarbon combustion reaction consist of carbon, hydrogen and oxygen.  In balancing the hydrocarbon combustion reaction at first carbon and hydrogen atoms are balanced and at last oxygen atoms are balanced.

Oxygen atoms are balanced at the end because oxygen atom stand alone as O2 and easier to balance than hydrogen and carbon.

Hence, the correct option is "A".

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).