Answer: 1. thunderous silence is an oxymoron, 2. dearly departed is an euphemism, 3. happy memory is a personification and 4. cool as ice is a simile.
Explanation: an oxymoron is a figure of speech where contradictory terms are used together (like "thunderous silence"). An euphemism is an indirect word or expression substituted for one considered to be too harsh when referring to something unpleasant or embarrassing (for example saying "dearly departed" referring to someone that passed away). Personification is giving human characteristics to nonhuman objects (like "happy memory"). And a simile is a comparison using the words "like" or "as" (for example "cool as ice").
