Final answer:
Lithium reacts quickly because it's a solid alkali metal known for its rapid reactivity, making it necessary to store it under mineral oil to prevent reactions with air and moisture. Option d.
Step-by-step explanation:
Lithium reacts so quickly because it is in the solid state and is known for rapid reactivity. The correct option from the given choices would be d) Solid; conductor; rapid reactivity. Lithium is classified as an alkali metal (Group 1), and it is renowned for its high reactivity, which increases with the atomic number within the group. This high reactivity is due to the ease of losing its lone valence electron. Additionally, lithium is so reactive with moisture and oxygen that it is stored under mineral oil to prevent contact with air. It also has the lowest density of any metal, which allows it to float in substances like paraffin oil.