The solid form of a substance is usually more dense than its liquid and gaseous forms. similarly the liquid form is usually more dense than the gaseous form.
which of these breaks this general density rule?
a. ice floating in a glass of water
b. vapor rising from a hot cup of tea
c. cooled magma sinking in a lava flow
d. a hot air balloon falling as the gas inside cools

A is the answer.

Ice is solid, however, water is liquid. Yet ice still floats which is less dense than water.

Hope this helps!

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic 

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is