Identify which of the following properties are typical of the non-metal elements in period 3 of the periodic table. I.   They are poor conductors of both heat and electricity.II.  They form negative ions by gaining one or more electrons.III. They have high melting points and boiling points.

The properties of non-metal elements in period 3 of the periodic table are as follows:

I. They are poor conductors of both heat and electricity: This is true. Non-metals are generally poor conductors of heat and electricity.

II. They form negative ions by gaining one or more electrons: This is also true. Non-metals tend to gain electrons to achieve a stable electron configuration, forming anions (negative ions).

III. They have high melting points and boiling points: This is generally false. Non-metals usually have lower melting and boiling points than metals. However, there are exceptions, such as carbon in the form of diamond or graphite.

So, properties I and II are typical of non-metal elements in period 3 of the periodic table, while property III is not.