`a)` iron + khí oxygen  $\xrightarrow{t^o}$  iron (II) oxide.

`b)` \(\rm m_{iron}+m_{oxygen}=m_{iron\ (II)\ oxide}\)

`c)` Thay số: \(\rm 9+m_{oxygen}=14\)

\(\rm\to m_{oxygen}=14-9=5\) gam.

`a)` Phương trình chữ: Iron `+` khí oxygen` \overset(t^o)(->)`  Iron `(II)` oxide 

`b)` `m_(Iron) + m_(Oxy g en)=m_{Iron(II)o x ide}`

`c) m_(Oxy g en)=m_{Iron(II)o x ide}-m_(Iron)=14-9=5(g)`