What is the classification for this reaction? so3 (g) + h2o (l) → h2so4 (aq)?

There are six common types of reactions:

1. Combination
2. Decomposition
3. Single Displacement
4. Double Displacement
5. Combustion
6. Redox

The reaction: SO₃₍g₎ + H₂O₍l₎ → H₂SO₄₍aq₎ is classified as a combination reaction. This is because for combination reactions, two (or more) reactants form a single product. On the other hand, decomposition reactions involve a single reactant breaking down into two or more simpler substances. Displacement reactions involve a more active element displacing a less active element from a compound. Meanwhile, combustion reactions involve a carbon-containing compound reacting with oxygen to form carbon dioxide and water. Redox reactions then involve exchange of electrons between species.  

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