Someone help me figure out this question

Why is it important always to use horizontal bars in unit fractions when performing unit conversions?

The diagram shows a series of volcanic island and a hot spot determine the direction of movement of the tectonic plate that for the island

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.