Why can a hydrogen atom form a covalent bond without fulfilling the octet rule?

The answer is: Hydrogen's valence shell can hold only up to two electrons.

Hydrogen (symbol: H) is a chemical element with atomic number 1, which means it has one proton and one electron.

Electron configuration of hydrogen atom: ₁H 1s¹.

In s orbital maximum number of electrons is two.

Hydrogen form bonds with electrons as closest noble gas helium (He).

e

explanation:

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.