$2.$ The $\_\_\_\_\_\_\_\_$ process converts straight$-$chain hydrocarbons to branched$-$chain hydrocarbons to improve the $\_\_\_\_\_\_$ number of gasoline. This process typically involves the use of $\_\_\_\_\_\_\_\_$ as a catalyst.

$($Options: isomerization, alkylation, cracking; viscosity, octane, cetane; zeolite, platinum, sulfuric acid$)$