6. Why does sound travel faster through a steel bar than through a swimming pool filled with water? Water is a denser medium than steel.
Water has a larger wavelength than steel.
Steel has a larger wavelength than water.
Steel is a denser medium than water.

I understand that sound travels faster in water then in air. Water is a liquid, and air is gas.

Water still has the ability to roll the molecules over each other (so water can flow), it has some flexibility.

But I do not understand how a solid that is inflexible can make sound waves travel faster then in a flexible liquid.

In fact, sound waves travel over 17 times faster through steel than through air.

Sound waves travel over four times faster in water than it would in air.

Since valence shells in nonmetal atoms are almost full, the atoms attract electrons and hold them tightly to fill their valence shells.

Explanation:

1) Insulating is the property of non permiting the flow of current.

2) The current is carried by electrons, so if the electrons move there is flow of current, and if the electrons do not move there is not flow of current and the material is an insulator.

3) The nonmetlas are in the righ part of the periodic table: columns 14 to 18 (but not the entire columns, column 14 has only 1 nonmetal, column 15 has two nonmetals, column 16 has 3 nonmetals, column 17 has 4 nonmetals, and column 18 has 7 nonmetals). Those elements have the valence shells almost full (which you can predict in virtue of ther positions in the periodic table) and so they are not willing to let the electrons to move freely from one atom to another, instead they prefer to keep their electrons and fill the valence shell (stable configuration).

Hence, the no flow of the electrons explains the insulating property.