(i) The compound `CH_(3)-CH_(2)-Br` has 2 carbon atoms so its parent hydrocarbon is ethane. This compound also has a bromo group `(Br)` attached to one carbon atom. So the name of this compound will be bromoethane.
(ii) The compound `(H-overset(H)-overset(|)(C)=O)` has 1 carbon atom, so its parent alkane is methane. It has an aldehyde group `(-overset(H)overset(|)(C)=O)` which is represented by the ending `al`. Now replacing the last `e` of methane by `al` the name of this compound becomes methanal.
(iii) The compound `H-underset(H)underset(|)overset(H)overset(|)(C)-H-underset(H)underset(|)overset(H)overset(|)(C)-H-underset(H)underset(|)overset(H)overset(|)(C)-H-underset(H)underset(|)overset(H)overset(|)(C)-C-=C-H` has 6 carbon atoms in it, so its parent alkane is hexane. It has also a triple bone `(-C-=C-)` in it which is indicated by the suffix yne. Now replacing the ane of hexane by yne the name of above compound becomes hexyne.