Answer
(a) $MgF_2$
(b) $SnO_2$
(c) $Fe_2S_3$
Work Step by Step
(a) Magnesium is represented by $Mg$, and fluoride is made of fluorine $F$.
$MgF$
As we can see in figure 2.15 (Page 61), $Mg$ has a charge of $2+$, so we multiply the number of fluorides by 2.
$MgF_2$
(b)
Tin is represented by $Sn$, and oxide ion is made of oxygen, $O$.
$SnO$
As we can see in its name, tin IV has a charge of $4+$, so we multiply the number of oxygens by 4.
As we can see in figure 2.15 (Page 61), $O$ has a charge of $2-$, so we multiply the number of tin by 2.
$Sn_4O_2$
Simplifying it: $Sn_2O$
(c)
Iron is represented by $Fe$, and sulfide ion is made of sulfur, $S$.
$FeS$
As we can see in its name, iron (III) has a charge of $3+$, so we multiply the number of sulfides by 3.
As we can see in figure 2.15 (Page 61), sulfide has a charge of $2-$, so we multiply the number of irons by 2.
$Fe_2S_3$
