What is usually released in a combustion reaction? . a. energy. b. elemental oxygen. c. a carbon-based fuel. d. elemental carbon.

A) energy

Explanation:

All combustion reactions are exothermic. This means that it releases energy when it happens, and that energy comes from the rupture of bonds between carbon atoms.

Also, carbon-based fuel and oxygen are usually the reactant of the combustion and carbon is always released as an oxide.

h

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.