Identify chiral and achiral molecules in each of the following pairs of compounds.

(A) molecule is chiral if it has a chiral center (a carbon atom bonded to four different groups). Otherwise,it is achiral.
$(i)$ $(i)$ $CH_3CH(Br)OH$: The central carbon is bonded to $-H$,$-CH_3$,$-Br$,and $-OH$. Since all four groups are different,it is chiral.
(ii) $CH_3CH(Br)_2$: The central carbon is bonded to two identical $-Br$ atoms. Thus,it is achiral.
(ii) $(i)$ $CH_3CH(OH)CH_2CH_2CH_3$: The carbon bonded to $-OH$ is attached to $-H$,$-CH_3$,$-OH$,and $-CH_2CH_2CH_3$. All four groups are different,so it is chiral.
(ii) $CH_3CH_2CH(OH)CH_2CH_3$: The carbon bonded to $-OH$ is attached to $-H$,$-OH$,and two identical $-CH_2CH_3$ groups. Since two groups are identical,it is achiral.
(iii) $(i)$ $CH_3CH(Br)CH_2CH_3$: The carbon bonded to $-Br$ is attached to $-H$,$-CH_3$,$-Br$,and $-CH_2CH_3$. All four groups are different,so it is chiral.
(ii) $CH_3CH_2CH_2CH_2Br$: The carbon bonded to $-Br$ is attached to two $-H$ atoms. Since two groups are identical,it is achiral.