Of the following compounds, (I) which ones exist as molecules, and (II) which ones manifest as extended structures spanning three dimensions?

NaCl, CO₂, SiO₂, BF₃

Explain the following: OF₆ does not form, but SF₆ does.

Among the Group 4A elements, only carbon has an allotrope with a diamond structure, while the rest have metallic allotropes. Is this statement true or false? If it is true, justify your answer. If otherwise, state the correct answer.

The main greenhouse gases are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and water vapor (H₂O). Arrange these substances in increasing boiling point and justify the arrangement.

Consider the positions of the following elements in the periodic table:

Determine the element that would form the oxide with the highest melting point and the lowest melting point.

Identify whether the following statement is true or false. Boron is the most abundant element in the earth's crust among group 3A elements.

Determine the most common oxidation states for each of the following elements: Boron, Aluminum, Gallium, Indium, and Thallium.

Which element–Si, In, O, or Br–is the best conductor of electricity?

Which of the following statements explains the differences between the properties of boron and the other Group 3A elements?

Consider the molecular models below as proposed structures of hydrides of second-row elements. For each structure that is possible, identify the nonhydrogen atom and write the molecular formula.

Describe the physical properties of the following substances: PH₃, CaH₂, and ZrH_1.9.

Identify the incorrect statement about hydrogen.