Explain why groups 14 and 15 are better representatives of mixed groups than groups 13 and 16.

Explanation:

Mixed groups are groups on the periodic table that contain more than one class (as in metals, non-metals or metalloids) of elements. Groups 13 to 16 form the mixed groups of the periodic table because they contain at least two different classes of elements.

However, groups 14 and 15 contain more classes (three classes) than groups 13 and 16 (two classes). Group-14 contains metals (examples include tin), non-metals (examples include carbon) and metalloids (examples include silicon) while group-15 also contains metals (such as bismuth), non-metals (such as nitrogen) and metalloids (such as arsenic). Whereas group 13 and 16 only contain two classes of elements; group-13 contains metalloid (boron) and metals (such as aluminium) while group-16 contains metalloids (such as tellurium) and non-metals (such as oxygen).

a) the particles of the chair are strongly held together.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.