# Stereochemistry of cycloalkanes having substituents

My teacher said that from $3$ to $6$ member cycloalkanes having any number and type of substituents we can always draw the planar structure and decide the specifics of stereochemistry like:

1. Are they optically active or not?
2. Are they meso compunds or not?
3. Do they have a plane of symmetry/centre of symmetry/axis of symmetry/alternating axis of symmetry or not?

But I feel that the molecules are hardly in planar form. It would be incorrect to assume they are planar and find the specifics of stereochemistry. Only for cyclopropane the points should be correct as it is always planar. Maybe my teacher said that mistakenly in a hurry.

So regarding points $(1),(2)$ and $(3)$ who is correct? Why? Or are we both partially correct? I need a slightly detailed answer.