Given structures $I$ and $II$ are:

In the Newman projection for $2,2$-dimethylbutane,what can $X$ and $Y$ respectively be?
$A$. $H$ and $H$
$B$. $H$ and $C_2H_5$
$C$. $C_2H_5$ and $H$
$D$. $CH_3$ and $CH_3$

What is the increasing order of stability for the three main conformers (e.g.,eclipsed,anti,gauche) of $2$-fluoroethanol?

Which of the structures $(a - d)$ will be produced if a "ring flip" occurs in the following compound in chair form?

Which is the most stable conformation of ethylene glycol?

$HO-CH_2-CH_2-CHO$
Which conformer of the above compound is most stable (consider the conformer across the $C_2-C_3$ bond)?