Question

hydrogenation is the addition of ______ to an alkene.
○ hydrogen (h)
○ hydrogen gas (h₂)
○ hydroxide (-oh)
○ water (h₂o)
○ hydrogen peroxide (h₂o₂)

Explanation:

Hydrogenation is a chemical reaction where hydrogen gas ($\ce{H_2}$) is added across a double bond (like in alkenes) in the presence of a catalyst. Hydrogen (H) is an atom, hydroxide (-OH) is a functional group, water ($\ce{H_2O}$) and hydrogen peroxide ($\ce{H_2O_2}$) don't participate in hydrogenation of alkenes in the same way. So the correct option is hydrogen gas ($\ce{H_2}$).

Answer:

B. hydrogen gas ($\ce{H_2}$) (assuming the options are labeled A - E in order, with this option being the second one; if labels differ, adjust to the correct label with the text "hydrogen gas ($\ce{H_2}$)")