Question

unit 5 comprehensive quiz l
the table below provides some information about an unidentified element.
physical properties
brittle
low melting point and boiling point
is a gas as at room temperature
chemical properties
highly reactive
reacts with sodium
based on this information, the unidentified element is best classified as which of the following?
h (hydrogen - atomic number 1)
cl (chlorine - atomic number 17)
k (potassium - atomic number 19)
he (helium - atomic number 2)

Explanation:

Step1: Analyze properties of each element

• H (Hydrogen):
• Physical: Gas at room - temperature, low melting and boiling points.
• Chemical: Reactive. But it is not highly reactive in the same sense as halogens. And its reaction with sodium is not as typical as that of halogens.
• Cl (Chlorine):
• Physical: Gas at room - temperature (\(Cl_2\) is a gas), brittle (as a solid, but in gas form we consider its general non - metallic brittleness in solid state analogy), low melting (\(-101.5^{\circ}C\)) and boiling (\(-34.04^{\circ}C\)) points.
• Chemical: Highly reactive (halogen). Reacts with sodium (\(2Na + Cl_2=2NaCl\)).
• K (Potassium):
• Physical: Solid at room - temperature (melting point \(63.5^{\circ}C\)), not brittle (metallic, malleable and ductile).
• Chemical: Reactive (alkali metal), but its physical properties do not match.
• He (Helium):
• Physical: Gas at room - temperature, low melting (\(-272.2^{\circ}C\)) and boiling (\(-268.934^{\circ}C\)) points.
• Chemical: Unreactive (noble gas).

Answer:

Cl (Chlorine - Atomic number 17)