Answer
Empirical formula: $Tb_2O_7$
Oxidation number: $+7$
Reaction: $4\ Tb(s)+7\ O_2(g)\rightarrow 2\ Tb_2O_7(s)$
Work Step by Step
In 100 g of the compound:
Tb: $73.945\ g/158.925\ g/mol=0.465\ mol$
O: $26.055\ g/15.999\ g/mol=1.62\ mol$
The ratio of the two:
$1.62/0.465=3.50=7/2$
Empirical formula:
$Tb_2O_7$
Oxidation number:
$0= x\times2-2\times7$
$x=+7$
Reaction:
$4\ Tb(s)+7\ O_2(g)\rightarrow 2\ Tb_2O_7(s)$
