Question

20. Which common element reacts quickly and violently if exposed to moisture, is a solid soft enough to be cut easily with a knife at room temperature, and melts at almost the exact temperature that water boils?

a. chlorine

c. iron

21. What is the atomic number of the element fluorine?

b. carbon

d. sodium

Answer 1

20. The element that reacts quickly and violently if exposed to moisture, is a solid soft enough to be cut easily with a knife at room temperature, and melts at almost the exact temperature that water boils is **d. sodium**. Sodium is known for its reactivity with water and has a melting point of about 98°C, which is close to the boiling point of water (100°C).

21. The atomic number of the element fluorine is **9**.