Halogen derivatives of alkanes are classified according to _____.

The reaction is:

${\text{R-CH}}_{\text{2}}\text{-OH + HCl }\stackrel{}{\to }{\text{R-CH}}_{\text{2}}{\text{-Cl+H}}_{\text{2}}\text{O}$

For the completion of the reaction, ______ is used.

In the compound $\text{'}\mathrm{X}\text{'}$, all the bond angles are exactly ${109}^{\circ }28\text{'}. \text{'}\mathrm{X}\text{'}$may be ______.